Table 5. Excitation Energiesa.
| 3B1u← 1Ag [eV] | 3A1← 1Ag [eV] | |
|---|---|---|
| VMC (all-ele) | 4.598(16) | 2.843(16) |
| VMC (SR-ECP) | 4.626(5) | 2.862(5) |
| VMC (HF-NCP) | 4.549(5) | 2.873(5) |
| VMC (SR-NCP) | 4.555(5) | 2.854(5) |
| LRDMC (all-ele) | 4.642(19) | 2.919(19) |
| LRDMC (SR-ECP) | 4.626(10) | 2.892(10) |
| LRDMC (HF-NCP) | 4.533(10) | 2.849(10) |
| LRDMC (SR-NCP) | 4.568(10) | 2.876(10) |
| CIS65 | 1.995 | |
| LDA34 | 4.874 | 2.953 |
| MP234 | 4.549 | 2.970 |
| B3LYP34 | 4.462 | 2.667 |
| MR-CI28 | 4.597 | 2.780 |
| CCSD(T)33 | 4.514 | 2.845 |
| DMC (HF-ECP)34 | 4.523(13) | 2.862(13) |
| DMC (CASSCF-ECP)34 | 4.488(13) | 2.879(13) |
| DMC (HFall)34 | 4.501(26) | 2.875(18) |
| DMC (GVB)31 | 4.6027(13) | 2.9102(61) |
| DMC (CAS2–2)66 | 4.49(2) | |
| PDb | 2.52(13) | |
| EELSc | 4.2 | |
| IISd | 4.3 | |
| EELSe | 4.32 | |
| OSf | 4.60 | |
| LEEISg | 4.68 |
a
The adiabatic excitation energy is corrected with the difference between the singlet and triplet zero point energies, which has been estimated to be 0.1388 eV (3.2 kcal/mol).33 The all-electron values reported are related to the 9s5p2d basis set with n = 12 molecular orbitals. The pseudopotential calculations all refer to the same (5s5p5d)/[1s2p1d] basis set for the carbon atom.
b
Photodissociation experiment ref 27.
c
Electron energy loose spectroscopy ref 25.
d
Ion impact spectroscopy ref 26.
e
Electron energy loose spectroscopy ref 67.
f
Optical absorption spectroscopy ref 21.
g
Low-energy electronimpact spectroscopy ref 24.