Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2023 Dec 20;128(1):73–80. doi: 10.1021/acs.jpca.3c05658

Theoretical Studies on the Isomerization Kinetics of Low-Lying Isomers of the SiC4H2 System

Nisha Job †, Vijayanand Chandrasekaran †, Venkatesan S Thimmakondu ‡,*, Krishnan Thirumoorthy †,*
PMCID: PMC10979431  PMID: 38116994

Abstract

graphic file with name jp3c05658_0012.jpg

The low-lying isomers of SiC4H2 are investigated to understand the kinetics of isomerization pathways using density functional theory. In our earlier work, we studied the various possible isomers (J. Phys. Chem. A, 2020, 124, 987–1002) and the chemical bonding of low-lying isomers of SiC4H2 (J. Phys. Chem. A, 2022, 126, 9366–9374). Among them, four isomers, 1-ethynyl-3-silacycloprop-1-en-3-ylidene (1), 3-silapent-1,4-diyn-3-ylidene (2), 1-silapent-1,2,3,4-tetraen-1-ylidene (4), and 1-silapent-2,4-diyn-1-ylidene (5) have already been identified in the laboratory. The previously known theoretical isomer 2-methylene-1-silabicyclo[1.1.0]but-1(3)-en-4-ylidene (3) and the newly identified unknown isomer through the present kinetic studies 5-silabicyclo[2.1.0]pent-1(4),2-dien-5-ylidene (N6) remain elusive in the laboratory to date. The isomerization pathways of the low-lying isomers of SiC4H2 are predicted through the transition state structures. Intrinsic reaction coordinate analysis identifies the minimum energy reaction pathways connecting the transition state from one isomer to another of the investigated system. The present kinetic data reveal the isomerization of global minimum energy isomer 1 to thermodynamically stable low-lying isomers, 2 and 5. Interestingly, isomer 3 interconverts to the experimentally known low-energy isomer 4, the second most thermodynamically stable isomer among them. The thermodynamic and kinetic parameters of the low-lying isomers of SiC4H2 are also documented in this work. The rate coefficient and equilibrium constant for isomerization reactions are calculated using the Rice–Ramsperger–Kassel–Marcus theory. The equilibrium constant delineates the difficulties in forming N6 and 3 through the isomerization pathways. Furthermore, ab initio molecular dynamics studies dictate the stability of low-lying isomers of SiC4H2 within the time scale of the simulation.

1. Introduction

In recent years, group 14 elements, such as carbon and silicon, have been found to be essential in advancing astrophysics and astrochemistry due to their proven existence in the interstellar medium (ISM) and circumstellar envelopes (CSEs).1−5 Molecules containing silicon account for roughly 10% of the molecular species in space. Specifically, silicon-bearing compounds are essential for gas-orbiting star-forming regions and late-type stars.6−9 Out of the 300 species identified in ISM and CSEs, 15 are Si-bearing species.10,11 One can understand the chemical evolution of carbon-rich CSEs through astronomical observations of these molecules and their astrochemical model exploiting intricate gas phase reaction networks.12−19 Complex organosilicon molecules are abundant in the asymptotic giant branch (AGB) CSEs, but their formation mechanisms remain an open debate.20−22 The significance of organosilicon molecules as precursors in forming silicon-carbide dust grains in CSE discharge has garnered special attention. It is unknown how the chemistry of silicon and carbon around stars has led to the formation of submicron-sized granules.23 Stellar winds and outflows cause evolved stars to lose mass in the latter phases of their evolution. These outflows may include silicon-bearing molecules, in addition to gas and dust. In addition, shock waves provide energy, and pressure conditions lead to the formation of these molecules.24−27 Hydrogenated organosilicon compounds may form due to the interaction between extruding molecules and the surrounding environment. The specific pathways and mechanisms for hydrogenated organosilicon compound formation are an ongoing new frontier in research. In previous studies, related elemental compositions such as SiC2H2, SiC3H2, SiC3H4, Si2CH2, Si2C5H2, and Si3C2H2 are studied, and plausible synthetic routes and spectroscopic parameters were either reported experimentally or theoretically.21−30 Till now, more than five hundred absorption bands called diffuse interstellar bands (DIBs) have been identified. Except for C60 and its cation, its carriers are unknown. It is widely accepted that the carriers of diffuse interstellar bands are molecules, mostly in the gas phase. Therefore, investigating more about these molecules in astronomical observations, laboratory experiments, and theoretical predictions will shed light on the formation of these intriguing compounds. Recent laboratory studies focus on the formation mechanism of SiC4H2 molecules in different pathways, including (i) diacetylene (C4H2) and silylidyne radical (SiH) single-collision and (ii) silicon and diacetylene bimolecular reactions, which are pursued in the laboratory investigations of SiC4H2 formation.31−39 Since one SiC4 isomer is already identified in the CSE,40 their hydrogenated derivatives, such as SiC4H2 isomers, are considered to have potential implications in astronomical identification.

The present work explores the dissociation pathways of low-lying isomers of SiC4H2 as shown in Figure 1, namely, 1-ethynyl-3-silacycloprop-1-en-3-ylidene (1), 3-silapent-1,4-diyn-3-ylidene (2), 2-methylene-1-silabicyclo[1.1.0]but-1(3)-en-4-ylidene (3), 1-silapent-1,2,3,4-tetraen-1-ylidene (4), 1-silapent-2,4-diyn-1-ylidene (5), and 5-silabicyclo[2.1.0]pent-1(4),2-dien-5-ylidene (N6). Maier and co-workers41 had trapped 1 and 2 in the Ar matrix at 10 K by flash pyrolysis of triethynylsilane [HSi(C2H)3] and 1,1-diethynyl 2,2,2-trimethyl disilane [Me3Si–SiH (C2H)2]. Isomer 5 is formed by irradiating 254 nm photons (4.88 eV) on isomers 1 and 2, causing photoisomerization.41 McCarthy and co-workers observed the rotational spectrum of isomer 4 in a pulsed supersonic molecular beam by Fourier transform microwave (FTMW) spectroscopy.42 In the same direction, thermochemistry and kinetic studies of SiC4H2 isomers on its potential energy surface (PES) are essential to understanding the possible rearrangements between various low-lying isomers and are explored in detail in the present work.

Figure 1.

Figure 1

Open in a new tab

Low-lying isomers of SiC4H2 at the B3LYP/6-311++G(2d,2p) level. (The naming convention of the isomers is followed as per the previously published papers. The experimentally detected isomers are marked with an asterisk).

In our earlier work, the possible isomers of SiC4H2 have been reported with different levels of theoretical methods43 and, later, explored the chemical bonding features of SiC4H2 isomers.44 Out of the reported isomers, 1 is a global minimum geometry, and all other isomers of SiC4H2 lie within 50 kcal/mol, which was well documented with their structural parameters. In continuation of our previous works, the present work aims to determine the isomerization pathways of low-lying isomers of SiC4H2. The relative energies (ΔE), activation energies (ΔE‡), zero-point vibrational energy corrections (ZPVE), and Gibbs free energies (G) for dissociation pathways of low-lying SiC4H2 isomers are presented here, which give glimpses of their thermodynamic and kinetic stabilities. The present theoretical studies on transition state structure predictions and their minimum-energy reaction paths are performed through intrinsic reaction coordinate (IRC) analysis, which provides insights into the kinetic stability of these isomers and their isomerization pathways through various rearrangements.

2. Computational Methodologies

The low-lying geometries of SiC4H2 isomers considered in this work were optimized using density functional theory (DFT) at the B3LYP45,46/6-311++G(2d,2p)47,48 level of theory. We identified the transition state structures for the predicted dissociation pathways of low-lying isomers of SiC4H2 at the same level of theory. Through frequency calculations at the same level, transition state structures were confirmed with one imaginary frequency. Furthermore, the predicted dissociation pathway for each isomer was established by intrinsic reaction coordinate (IRC)49,50 calculations and was carried out at the same level. All the computational calculations were carried out with the Gaussian suite of programs.51 To investigate the kinetic stability of isomers, we executed ab initio molecular dynamics (AIMD) simulations using the atom-centered density matrix propagation (ADMP)52 method implemented in the Gaussian 16 program.51 The rate coefficients for the isomerization reaction were calculated using Rice–Ramsperger–Kassel–Marcus (RRKM) theory53 using the following equation

2.

where ETS is the energy of the transition state from the ground state of the isomers under consideration, E is the total energy of the isomer, N(E – ETS) is the sum of states of the transition state that would be available for the given energy E of the isomer, c is the velocity of light, and ρ is the density of the vibrational states. The Beyer–Swinehart (BS) algorithm is a direct count method to calculate the vibrational density of states.54 In this approach, the density of states was calculated by summating all of the energies of the individual harmonic oscillator for a particular energy. In this work, harmonic vibrational frequencies were used for calculating the level densities for each isomer, and the bin size for the calculation was kept as 1 cm–1.

3. Results and Discussion

3.1. Isomerization Pathways

The reaction energy profile for the isomerization of 1 to 5 is shown in Figure 2. The dissociation pathway, type-A in 1, leads to 5 with an activation barrier of 57.8 kcal/mol. The IRC calculation for the isomerization pathway of 1 to 5 is shown in Figure 3, which reveals that the identified transition state structure (TSA1) connects both 1 and 5 through the minimum energy reaction path. The formation of 5 happens by breaking the Si–C single bond in 1. The optimized geometrical parameters for the isomerization pathway of 1 to 5 and its corresponding TSA1 are compared in Table S1. From the reaction energy profile, it is clear that the formation of 5 from 1 is endothermic. Furthermore, the identified transition state, TSA2, also connects the global minimum geometry 1 and 5. The optimized geometrical parameters for the isomerization pathway of 1 to 5 and its corresponding TSA2 are compared in Table S2. The computed results of the reaction energy profile predict that the mechanism behind the irradiation of 1 is specifically produced by 5 rather than other low-lying isomers.

Figure 2.

Figure 2

Open in a new tab

Reaction energy profiles for the isomerization of 1 to 5. The ZPVE-corrected relative energy is in kcal/mol.

Figure 3.

Figure 3

Open in a new tab

IRC for the isomerization pathway of 1 to 5.

On the other hand, the dissociation pathway of type-B in 1 leads to the formation of 2. The reaction energy profile for the isomerization pathway of 1 to 2 is shown in Figure 4. The identified transition state structure (TSB) for the isomerization of 1 to 2 follows an IRC pathway by connecting them through a minimum energy reaction path, as shown in Figure 5. The required activation energy for the isomerization of 2 from 1 is 70.9 kcal/mol. From this barrier height, one can conclude that 1 and 2 are the most kinetically stable isomers. Isomer 2 is an endothermic product when compared to 1. The formation of 2 can happen by breaking the Si–C single bond in 1 through the dissociation pathway of type-B. The optimized geometrical parameters for the isomerization pathway of 1 to 2 and its corresponding transition state structure are listed in Table S3.

Figure 4.

Figure 4

Open in a new tab

Reaction energy profile for the isomerization pathway of 1 to 2. The ZPVE-corrected relative energy is in kcal/mol.

Figure 5.

Figure 5

Open in a new tab

IRC for the isomerization pathway of 1 to 2.

The schematic reaction energy profile for the formation of N6 is shown in Figure 6. The identified transition state structure for the formation of N6 from 2 connects the minimum energy IRC path, as shown in Figure 7. The energy and geometry of the isomers in this reaction pathway are well connected to the IRC path. The predicted transition state structure for forming N6 from 2 is a fused three-membered and four-membered ring with four carbon atoms formed through the radical mechanism. The required activation energy barrier for the reaction pathway is 74.1 kcal/mol, and the reaction is highly endothermic; thus, it dictates that 2 is a kinetically stable isomer. It is noted here that isomer N6 is identified through present kinetic studies and is not reported elsewhere. The energy-minimized geometrical parameters for the isomerization pathway of 2 to N6 and its corresponding transition state are provided in Table S4.

Figure 6.

Figure 6

Open in a new tab

Schematic reaction energy profile for the formation of N6. The ZPVE-corrected relative energy is in kcal/mol.

Figure 7.

Figure 7

Open in a new tab

IRC for the isomerization pathway of 2 to N6.

The isomerization pathways of type-C and type-D for the formation of 4 from 3 are shown in Figure 8. The dissociation of the Si–C bond in 3 leads to the second most thermodynamically stable isomer 4, which is an exothermic product. The identified transition state structure (TSC) through the dissociation pathway of type-C for forming 4 is well connected with its minimum energy path, as shown in Figure 9. The energy-minimized geometrical parameters for the isomerization pathway of 3 to 4 with TSC are provided in Table S5.

Figure 8.

Figure 8

Open in a new tab

Schematic reaction energy profiles for the formation of 4 from 3. The ZPVE-corrected relative energy is in kcal/mol.

Figure 9.

Figure 9

Open in a new tab

IRC for the isomerization pathway of 3 to 4.

The activation energy required through this pathway for the formation of 4 from 3 is 15.5 kcal/mol. Furthermore, isomer 3 also connects to 4 through another transition state (TSD) structure. The calculated activation energy barrier for the conversion of 3 to 4 with TSD is 11.4 kcal/mol. The energy-minimized geometrical parameters for the isomerization pathway of 3 to 4 with TSD are provided in Table S6. Although the type-D pathway appears energetically favorable for the formation of 4 as an exothermic product, we leave this discussion with a caveat that our AIMD calculations on the other hand have indicated that isomer 3 is also a kinetically stable molecule awaiting experimental confirmation. The Cartesian coordinates of all of the low-energy isomers and their corresponding transition state structures are provided in Tables S7 and S8, respectively, obtained at the B3LYP/6-311++G(2d,2p) level of theory.

3.2. Rate Coefficient for the Isomerization Reaction

As mentioned previously, isomers 1, 2, 4, and 5 are observed experimentally. However, isomers 3 and N6 have not been identified in the laboratory until today. Therefore, the rate coefficients for investigated isomerization reactions are calculated to delineate the possibilities of finding these isomers in the experimental laboratory observations. As an energy function, the rate of isomerization reactions for 1 to 5, 1 to 2, and 3 to 4 are given in Figure 10. From the calculated rate coefficients, the equilibrium constant, the ratio of the forward to the reverse isomerization reactions, is calculated and provided as support information in Figure S1. The equilibrium constant is ∼1 order for the isomerization pathways of 1 and 5, illustrating that the formation of both isomers is equally possible. In the case of 1 and 2, the equilibrium constant is ∼10, indicating that the forward reaction (1 to 2) is 10 times faster than the backward reaction. Thus, the possible existence of isomer 1 is higher than 2. Furthermore, the calculated rates for the isomerization of 2 to N6 are provided. For these isomers, the rate of the isomerization between N6 to 2 (reverse reaction) is several orders of magnitude faster than the rate of isomerization between 2 to N6.

Figure 10.

Figure 10

Open in a new tab

Rate coefficient for the forward and reverse isomerization reactions of (a) 1 and 5, (b) 1 and 2, (c) 3 and 4, and(d) 2 and N6.

Similarly, the isomerization rate from 3 to 4 with TSC or TSD is faster than the pathway of 4 to 3, indicating that it reverts to 4. This result reiterates the fact that, from a kinetic perspective, isomer 4 is kinetically more stable compared to 3. Therefore, the possibilities of existing isomers 2 and 4 isomerizing to N6 and 3 are significantly lower, which is easily understood from the equilibrium constant values. This may be one of the reasons why both N6 and 3 have not been observed experimentally to date.

Overall, the isomerization pathways between the low-lying isomers of SiC4H2 are well documented here. The formation of 4 from 3 is kinetically and thermodynamically the most favorable pathway among the investigated isomers. Furthermore, this work shows that low-lying isomers of SiC4H2 can easily undergo potential rearrangements through Si–C bond dissociations. As per the experimentally observed isomerization in the Ar matrix at 10 K by Maier et al.,41 three-body interactions in the matrix can stabilize isomerized molecules when irradiated by 254 nm photons, thus stabilizing higher energy isomers. However, in ISM, three-body interactions are absent. Hence, this experimental method does not reproduce the actual astronomical environment. Even though the studied isomerization pathways may not be directly comparable with experimental protocols, they can help to predict the stability of these isomers. Therefore, the reverse reactions are important, which may hint at the stability of these isomers in the ISM.

3.3. Ab Initio Molecular Dynamics

Ab initio molecular dynamics simulations are carried out to demonstrate the stability of the lowest-lying isomers of SiC4H2 and also to determine whether these isomers would remain stable under the ISM conditions. The ADMP method,52 implemented in the Gaussian 16 program,51 was used to perform these calculations. These simulations were performed at 10 K and 1 atm pressure for 1000 fs. The time evolutions with total energies for the six isomers are depicted in Figure 11. In addition, snapshots at intervals of 250 fs are provided to analyze each isomer’s geometric changes within the simulation time scale. These data illustrate steady geometries across the whole period and a balanced oscillation of energies; thus, it indicates isomerization does not occur quickly, complimenting the high energy activation barriers of the potential energy surface profile of the isomerization process. As a result, it is also possible to deduce that these molecules are kinetically stable.

Figure 11.

Figure 11

Open in a new tab

Total energy evolution of isomers 1, 2, 3, 4, 5, and N6 of SiC4H2 obtained from the AIMD simulation carried out at 10 K and 1 atm pressure at the UB3LYP/6-311++G(2d,2p) level.

The formation of 4 from 3 follows an exothermic profile and is the most favorable pathway among the investigated isomers. Although this indirectly implies that isomer 3 is kinetically less stable compared to 4 through the proposed isomerization pathway, the molecular dynamics study of isomer 3 indicates that it is a kinetically stable molecule as such under cold conditions. At around 500 fs (see Figure 11), the Si–C bond breaks but then reforms again after a specific time (750 fs). Thus, one could conclude that 3 is also a kinetically stable molecule through AIMD simulation studies.

4. Conclusions

The low-lying isomers of SiC4H2 and their dissociation pathways with Si–C bond breaking in each isomer are theoretically investigated. Thermodynamically, all the isomers lie within ∼50 kcal/mol. The dissociation pathways of these isomers are predicted through transition state structure identification and are further confirmed by IRC calculations. These isomers’ kinetic and thermodynamic stabilities are well addressed through quantum chemical calculations. Isomers 1, 2, 4, and 5 were reported in the laboratory, whereas 3 and N6 remain elusive. Thermodynamically, isomers 3 and 5 are equally stable because they are not energetically well separated from each other. Also, the proposed isomerization pathway suggests that isomer 4 is kinetically more stable compared to isomer 3. Nevertheless, the molecular dynamics data of isomer 3 indicate that it is also a kinetically stable molecule since the Si–C bond breaks but then reforms again after a specific time. Therefore, the question is whether the formation of 3 in the electrical gas chamber is possible by utilizing new precursor molecules. The calculated rate coefficients and equilibrium constant values elucidate the experimental difficulties in finding N6 in the laboratory. This may be because N6 will quickly revert to 2 according to the proposed isomerization pathways. Furthermore, the present theoretical work is expected to encourage and support experimental chemists in developing practical synthetic approaches and characterizing these putative isomers in terrestrial laboratory environments.

Acknowledgments

This research received no specific grant from public, commercial, or not-for-profit funding agencies. However, the computational facility provided in VIT, Vellore, through a research grant by the Department of Science and Technology (DST), Science and Engineering Research Board (SERB), India (ref: YSS/2014/001019) is gratefully acknowledged. Computational support provided at the SDSU (for V.S.T.) by DURIP Grant W911NF-10-1-0157 from the U.S. Department of Defense and NSF CRIF Grant CHE-0947087 is gratefully acknowledged.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpca.3c05658.

  • Optimized structural parameters of isomers and transition state structures obtained at the B3LYP/6-311++G (2d, 2p) level; Cartesian coordinates of the optimized geometries; total electronic energies, zero-point vibrational energies, free energies, and relative energies calculated at the B3LYP/6-311++G (2d, 2p) level; and rate coefficient for the isomerization reaction (PDF)

The authors declare no competing financial interest.

Supplementary Material

jp3c05658_si_001.pdf (424.6KB, pdf)

References

  1. Redondo P.; Barrientos C.; Largo A. Theoretical Study of the Structures and Stabilities of AlCn, AlCn+, and AlCn- (n = 1–7) Monocyclic Clusters. Int. J. Quantum Chem. 2004, 96 (6), 615–626. 10.1002/qua.10756. [DOI] [Google Scholar]
  2. Sofia U. J.; Cardelli J. A.; Savage B. D. The Abundant Elements in Interstellar Dust. Astrophys. J. 1994, 430 (May), 650. 10.1086/174438. [DOI] [Google Scholar]
  3. Accolla M.; Santoro G.; Merino P.; Martínez L.; Tajuelo-Castilla G.; Vázquez L.; Sobrado J. M.; Agúndez M.; Jiménez-Redondo M.; Herrero V. J.; et al. Silicon and Hydrogen Chemistry under Laboratory Conditions Mimicking the Atmosphere of Evolved Stars. Astrophys. J. 2021, 906 (1), 44. 10.3847/1538-4357/abc703. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Henning T. Cosmic Silicates. Annu. Rev. Astron. Astrophys. 2010, 48 (1), 21–46. 10.1146/annurev-astro-081309-130815. [DOI] [Google Scholar]
  5. Waters L. B. F. M.; Molster F. J.; de Jong T.; Beintema D. A.; Waelkens C.; Boogert A. C. A.; Boxhoorn D.-R.; de Graauw T.; Drapatz S.; Feuchtgruber H.; et al. Mineralogy of Oxygen-Rich Dust Shells. Astron. Astrophys. 1996, 315, L361–L364. [Google Scholar]
  6. Iraqi M.; Schwarz H. Gas-Phase Generation and Characterization of Linear Silicon Carbon Hydrides SiCxH. (x = 4, 6) by Neutralization-Reionization Mass Spectrometry. Chem. Phys. Lett. 1993, 205 (2–3), 183–186. 10.1016/0009-2614(93)89226-8. [DOI] [Google Scholar]
  7. Yang T.; Bertels L.; Dangi B. B.; Li X.; Head-Gordon M.; Kaiser R. I. Gas Phase Formation of C-SiC 3 Molecules in the Circumstellar Envelope of Carbon Stars. Proc. Natl. Acad. Sci. U.S.A. 2019, 116 (29), 14471–14478. 10.1073/pnas.1810370116. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Parker D. S. N.; Wilson A. V.; Kaiser R. I.; Mayhall N. J.; Head-Gordon M.; Tielens A. G. G. M. On the Formation of Silacyclopropenylidene (c-SiC2H2) and Its Role in the Organosilicon Chemistry in the Interstellar Medium. Astrophys. J. 2013, 770 (1), 33. 10.1088/0004-637X/770/1/33. [DOI] [Google Scholar]
  9. McCarthy M. C.; Apponi A. J.; Gottlieb C. A.; Thaddeus P. Laboratory Detection of Five New Linear Silicon Carbides: SiC3, SiC5, SiC6, SiC7, and SiC8. Astrophys. J. 2000, 538 (2), 766–772. 10.1086/309177. [DOI] [Google Scholar]
  10. Paul D.; Sun B.-J.; He C.; Yang Z.; Goettl S. J.; Yang T.; Zhang B.-Y.; Chang A. H. H.; Kaiser R. I. Competing Si 2 CH 4 -H 2 and SiCH 2 -SiH 4 Channels in the Bimolecular Reaction of Ground-State Atomic Carbon (C(3 P j)) with Disilane (Si 2 H 6, X 1 A 1g) under Single Collision Conditions. J. Phys. Chem. A 2023, 127 (8), 1901–1908. 10.1021/acs.jpca.2c08417. [DOI] [PubMed] [Google Scholar]
  11. Müller H. S. P.; Thorwirth S.; Roth D. A.; Winnewisser G. The Cologne Database for Molecular Spectroscopy, CDMS. Astron. Astrophys. 2001, 370 (3), L49–L52. 10.1051/0004-6361:20010367. [DOI] [Google Scholar]
  12. Brenner V.; Milli P.; Bertolus M. Can We Rationalize the Structure of Small Silicon-Carbon Clusters?. Eur. Phys. J. D 1998, 1 (2), 197–205. 10.1007/s100530050081. [DOI] [Google Scholar]
  13. Botschwina P. An Accurate Equilibrium Structure and CCSD(T) Spectroscopic Constants for Linear C3Si2. J. Mol. Spectrosc. 1999, 198 (1), 192–193. 10.1006/jmsp.1999.7938. [DOI] [PubMed] [Google Scholar]
  14. Gordon V. D.; Nathan E. S.; Apponi A. J.; McCarthy M. C.; Thaddeus P.; Botschwina P. Structures of the Linear Silicon Carbides SiC4 and SiC6: Isotopic Substitution and Ab Initio Theory. J. Chem. Phys. 2000, 113 (13), 5311–5320. 10.1063/1.1290126. [DOI] [Google Scholar]
  15. Botschwina P.; Schulz B.; Oswald R.; Stoll H. A Theoretical Investigation of the Silicon-Carbon Chain Molecule SiC8. Z. Phys. Chem. 2000, 214 (6), 797. 10.1524/zpch.2000.214.6.797. [DOI] [Google Scholar]
  16. Ding X. D.; Wang S. L.; Rittby C. M. L.; Graham W. R. M. Fourier-transform infrared observation of SiCn chains. I. The ν4(σ) mode of linear SiC9 in Ar at 10 K. J. Chem. Phys. 1999, 110 (23), 11214–11220. 10.1063/1.479062. [DOI] [Google Scholar]
  17. Pellarin M.; Ray C.; Lermé J.; Vialle J. L.; Broyer M.; Blase X.; Kéghélian P.; Mélinon P.; Perez A. Photolysis Experiments on SiC Mixed Clusters: From Silicon Carbide Clusters to Silicon-Doped Fullerenes. J. Chem. Phys. 1999, 110 (14), 6927–6938. 10.1063/1.478598. [DOI] [Google Scholar]
  18. Duan X.; Burggraf L. W.; Weeks D. E.; Davico G. E.; Schwartz R. L.; Lineberger W. C. Photoelectron Spectroscopy of Si2C3- and Quantum Chemistry of the Linear Si2C3 Cluster and Its Isomers. J. Chem. Phys. 2002, 116 (9), 3601–3611. 10.1063/1.1427709. [DOI] [Google Scholar]
  19. Botschwina P.; Eugenia Sanz M.; McCarthy M. C.; Thaddeus P. Ab Initio Theory and Rotational Spectra of Linear Carbon Chains SiCnS. J. Chem. Phys. 2002, 116 (24), 10719–10729. 10.1063/1.1473807. [DOI] [Google Scholar]
  20. Thaddeus P.; Cummins S. E.; Linke R. A. Identification of the SiCC Radical toward IC + 10216—The First Molecular Ring in an Astronomical Source. Astrophys. J. 1984, 283, L45. 10.1086/184330. [DOI] [Google Scholar]
  21. Cernicharo J.; Gottlieb C. A.; Guelin M.; Thaddeus P.; Vrtilek J. M. Astonomical and Laboratory Detection of the SiC Radical. Astrophys. J. 1989, 341, L25. 10.1086/185449. [DOI] [Google Scholar]
  22. McCarthy M. C.; Gottlieb C. A.; Cernicharo J. Building Blocks of Dust: A Coordinated Laboratory and Astronomical Study of the Archtype AGB Carbon Star IRC+10216. J. Mol. Spectrosc. 2019, 356, 7–20. 10.1016/j.jms.2018.11.018. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Yang T.; Dangi B. B.; Kaiser R. I.; Bertels L. W.; Head-Gordon M. A Combined Experimental and Theoretical Study on the Formation of the 2-Methyl-1-Silacycloprop-2-Enylidene Molecule via the Crossed Beam Reactions of the Silylidyne Radical (SiH; X2) with Methylacetylene (CH3CCH; X1A1) and D4-Methylacetylene (CD3CCD; X1A1. J. Phys. Chem. A 2016, 120 (27), 4872–4883. 10.1021/acs.jpca.5b12457. [DOI] [PubMed] [Google Scholar]
  24. Tielens A. G. G. M.; The Physics and Chemistry of the Interstellar Medium; Cambridge University Press, 2005, pp 396–416. 10.1017/CBO9780511819056. [DOI] [Google Scholar]
  25. Tielens A. G. G. M. The Molecular Universe. Rev. Mod. Phys. 2013, 85 (3), 1021–1081. 10.1103/RevModPhys.85.1021. [DOI] [Google Scholar]
  26. Van Dishoeck E. F.; Herbst E.; Neufeld D. A. Interstellar Water Chemistry: From Laboratory to Observations. Chem. Rev. 2013, 113 (12), 9043–9085. 10.1021/cr4003177. [DOI] [PubMed] [Google Scholar]
  27. Tielens A. G. G. M.; Hollenbach D. Photodissociation Regions. I - Basic Model. II - A Model for the Orion Photodissociation Region. Astrophys. J. 1985, 291 (4), 722. 10.1086/163111. [DOI] [Google Scholar]
  28. Maier G.; Pacl H.; Reisenauer H. P.; Meudt A.; Janoschek R. Silacyclopropyne: Matrix Spectroscopic Identification and Ab Initio Investigations. J. Am. Chem. Soc. 1995, 117 (51), 12712–12720. 10.1021/ja00156a008. [DOI] [Google Scholar]
  29. Thirumoorthy K.; Chandrasekaran V.; Cooksy A. L.; Thimmakondu V. S. Kinetic Stability of Si2C5H2 Isomer with a Planar Tetracoordinate Carbon Atom. Chemistry 2020, 3 (1), 13–27. 10.3390/chemistry3010002. [DOI] [Google Scholar]
  30. Thimmakondu V. S.; Thirumoorthy K. Si3C2H2 Isomers with a Planar Tetracoordinate Carbon or Silicon Atom(S). Comput. Theor. Chem. 2019, 1157, 40–46. 10.1016/j.comptc.2019.04.009. [DOI] [Google Scholar]
  31. Wu Q.; Simmonett A. C.; Yamaguchi Y.; Li Q.; Schaefer H. F. Silacyclopropenylidene and Its Most Important SiC2H2 Isomers. J. Phys. Chem. C 2010, 114 (12), 5447–5457. 10.1021/jp905898j. [DOI] [Google Scholar]
  32. Kaiser R. I.; Krishtal S. P.; Mebel A. M.; Kostko O.; Ahmed M. An Experimental and Theoretical Study of the Ionization Energies of SiC2Hx(x = 0, 1, 2) Isomers. Astrophys. J. 2012, 761 (2), 178. 10.1088/0004-637X/761/2/178. [DOI] [Google Scholar]
  33. Schriver G. W.; Fink M. J.; Gordon M. S. Ab Initio Calculations on Some C3SiH4 Isomers. Organometallics 1987, 6 (9), 1977–1984. 10.1021/om00152a024. [DOI] [Google Scholar]
  34. Yang T.; Dangi B. B.; Maksyutenko P.; Kaiser R. I.; Bertels L. W.; Head-Gordon M. Combined Experimental and Theoretical Study on the Formation of the Elusive 2-Methyl-1-Silacycloprop-2-Enylidene Molecule under Single Collision Conditions via Reactions of the Silylidyne Radical (SiH; X2) with Allene (H2CCCH2; X1A1) and D4-Allene (D2CCC. J. Phys. Chem. A 2015, 119 (50), 12562–12578. 10.1021/acs.jpca.5b09773. [DOI] [PubMed] [Google Scholar]
  35. Jemmis E. D.; Prasad B. V.; Tsuzuki S.; Tanabe K. Analogy between Trivalent Boron and Divalent Silicon. J. Phys. Chem. 1990, 94 (14), 5530–5535. 10.1021/j100377a023. [DOI] [Google Scholar]
  36. Wu Q.; Hao Q.; Yamaguchi Y.; Li Q.; Fang D. C.; Schaefer H. F. Unusual Isomers of Disilacyclopropenylidene (Si2CH2). J. Phys. Chem. A 2010, 114 (26), 7102–7109. 10.1021/jp912280z. [DOI] [PubMed] [Google Scholar]
  37. Maier G.; Reisenauer H. P.; Pacl H. C2H2Si-Isomere: Erzeugung Durch Gepulste Blitzpyrolyse Und Matrixspektroskopische Identifizierung. Angew. Chem. 1994, 106 (12), 1347–1349. 10.1002/ange.19941061226. [DOI] [Google Scholar]
  38. Yang Z.; Doddipatla S.; Kaiser R. I.; Nikolayev A. A.; Azyazov V. N.; Mebel A. M. On the Synthesis of the Astronomically Elusive 1-Ethynyl-3-Silacyclopropenylidene (c-SiC4H2) Molecule in Circumstellar Envelopes of Carbon-rich Asymptotic Giant Branch Stars and Its Potential Role in the Formation of the Silicon Tetracarbide Chain (SiC4). Astrophys. J. 2021, 908 (2), L40. 10.3847/2041-8213/abde36. [DOI] [Google Scholar]
  39. Yang Z.; Doddipatla S.; He C.; Goettl S. J.; Kaiser R. I.; Jasper A. W.; Gomes A. C. R.; Galvão B. R. L. Can Third-Body Stabilisation of Bimolecular Collision Complexes in Cold Molecular Clouds Happen?. Mol. Phys. 2022, e2134832 10.1080/00268976.2022.2134832. [DOI] [Google Scholar]
  40. Ohishi M.; Kaifu N.; Kawaguchi K.; Murakami A.; Saito S.; Yamamoto S.; Ishikawa S.-I.; Fujita Y.; Shiratori Y.; Irvine W. M. Detection of a New Circumstellar Carbon Chain Molecule, C4Si. Astrophys. J. 1989, 345 (1), L83. 10.1086/185558. [DOI] [Google Scholar]
  41. Maier G.; Reisenauer H. P.; Meudt A. Silylenes of the Elemental Composition C4H2Si: Generation and Matrix-Spectroscopic Identification. Eur. J. Org Chem. 1998, 1998 (7), 1285–1290. . [DOI] [Google Scholar]
  42. McCarthy M. C.; Thaddeus P. The Rotational Spectra of H2CCSi and H2C4Si. J. Mol. Spectrosc. 2002, 211 (2), 228–234. 10.1006/jmsp.2001.8467. [DOI] [Google Scholar]
  43. Job N.; Karton A.; Thirumoorthy K.; Cooksy A. L.; Thimmakondu V. S. Theoretical Studies of SiC4H2 Isomers Delineate Three Low-Lying Silylidenes Are Missing in the Laboratory. J. Phys. Chem. A 2020, 124 (5), 987–1002. 10.1021/acs.jpca.9b11742. [DOI] [PubMed] [Google Scholar]
  44. Job N.; Thirumoorthy K. Chemical Bonding Perspective on Low-Lying SiC 4 H 2 Isomers: Conceptual Quantum Chemical Views. J. Phys. Chem. A 2022, 126 (50), 9366–9374. 10.1021/acs.jpca.2c06230. [DOI] [PubMed] [Google Scholar]
  45. Lee C.; Yang W.; Parr R. G. Development of the Colle-Salvetti Correlation-Energy Formula Into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785–789. 10.1103/physrevb.37.785. [DOI] [PubMed] [Google Scholar]
  46. Becke A. D. Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior. Phys. Rev. A 1988, 38, 3098–3100. 10.1103/PhysRevA.38.3098. [DOI] [PubMed] [Google Scholar]
  47. Krishnan R.; Binkley J. S.; Seeger R.; Pople J. A. Self-Consistent Molecular Orbital Methods. XX. A Basis Set for Correlated Wave Functions. J. Chem. Phys. 1980, 72 (1), 650–654. 10.1063/1.438955. [DOI] [Google Scholar]
  48. Clark T.; Chandrasekhar J.; Spitznagel G. W.; Schleyer P. V. R. Efficient Diffuse Function-Augmented Basis Sets for Anion Calculations. III. The 3-21+G Basis Set for First-Row Elements, Li-F. J. Comput. Chem. 1983, 4, 294–301. 10.1002/jcc.540040303. [DOI] [Google Scholar]
  49. Deng L.; Ziegler T.; Fan L. A Combined Density Functional and Intrinsic Reaction Coordinate Study on the Ground State Energy Surface of H2CO. J. Chem. Phys. 1993, 99 (5), 3823–3835. 10.1063/1.466129. [DOI] [Google Scholar]
  50. Deng L.; Ziegler T. The Determination of Intrinsic Reaction Coordinates by Density Functional Theory. Int. J. Quantum Chem. 1994, 52 (4), 731–765. 10.1002/qua.560520406. [DOI] [Google Scholar]
  51. Frisch M. J.; Trucks G. W.; Schlegel H. B.; Scuseria G. E.; Robb M. A.; Cheeseman J. R.; Scalmani G.; Barone V.; Petersson G. A.; Nakatsuji H.; et al. Gaussian 16, Revision B.01; Gaussian Inc. Gaussian Inc.: Wallingford, CT, USA, 2016.
  52. Schlegel H. B.; Millam J. M.; Iyengar S. S.; Voth G. A.; Daniels A. D.; Scuseria G. E.; Frisch M. J. Ab Initio Molecular Dynamics: Propagating the Density Matrix with Gaussian Orbitals. J. Chem. Phys. 2001, 114, 9758–9763. 10.1063/1.1372182. [DOI] [Google Scholar]
  53. Petrie S.; Herbst E. Some Interstellar Reactions Involving Electrons and Neutral Species: Attachment and Isomerization. Astrophys. J. 1997, 491 (1), 210–215. 10.1086/304941. [DOI] [Google Scholar]
  54. Beyer T.; Swinehart D. F. Algorithm 448: Number of Multiply-Restricted Partitions. Commun. ACM 1973, 16 (6), 379. 10.1145/362248.362275. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

jp3c05658_si_001.pdf (424.6KB, pdf)

Articles from The Journal of Physical Chemistry. a are provided here courtesy of American Chemical Society

RESOURCES