Table 3.

Summary of molecules (other than H₂ and CO) observed in disks and abundances derived.

Species	Spectral signature, region probed	Detection rate, abundance, and references
		T Tauri		Herbig Ae/Be
H2O	IR emission, inner atmosphere	many disks (0.4 − 800) × 1018 cm−2	(1,2,3,4,5,6,7,8,9,10,11) (6,7)	one disk: HD 163296 1014 − 1015 cm−2	(4,7,11,12,13,14,15) (14)
	sub-mm emission, outer disk	two disks: TW Hya, DGTau ~ 10−7 relative to H2	(16,17,18) (16)	one disk: HD 100546	(18,19)
OH	IR emission, inner atmosphere	many disks (0.4 − 200) × 1015 cm−2	(2,3,4,6,7,8,11,15,20) (6,7)	a dozen of disks (0.01 − 200) x 1015 cm−2	(4,7,11,12,21) (12,15,21)
C2H2	IR emission/absorption, inner disk	many disks (0.5 − 70) × 1015 cm−2	(2,6,7,8,22,23,24) (6,7,22,23,24)	none
HCN	IR emission/absorption, inner disk	many disks (0.5 − 65) × 1015 cm−2	(2,6,7,8,22,23,24) (6,7,22,23,24)	none
	mm emission, outer disk	many disks (0.2 − 10.6) × 1012 cm−2	(27,28,29,30,31,32,33,35) (28,31,32,33)	many disks (0.1 − 1) × 1012 cm−2	(28,29,30,31,32,33,34) (31,33,34)
HNC	mm emission, outer disk	two disks: DM Tau, TW Hya HNC/HCN = 0.3-0.4	(27,36) (27)	one disk: HD 163296 HNC/HCN = 0.1 − 0.2	(36) (36)a
CH4	IR absorption, inner disk	one disk: GV Tau 2.8 × 1017 cm−2	(25) (25)	none
CO2	IR emission/absorption, inner disk	many disks (0.04 − 10) × 1016cm−2	(6,7,22,24,26) (7,22,24,26)	one disk: HD 101412 1016 cm−2	(7) (7)
C2H	mm emission, outer disk	many disks (0.4 − 8.5) × 1013cm−2	(27,32,33,37,38) (33,37)b	two disks: AB Aur, MWC 480 (0.6 − 1) × 1013 cm−2	(33,34,37,39,40) (33)
CN	mm emission, outer disk	many disks (0.7 − 11.5) × 1013 cm−2	(27,28,29,30,31,32,33) (28,31,32,33)	a handful of disks (0.1 − 1.5) × 1013 cm−2	(28,29,30,31,33,34) (28,31,33,34)
H2CO	mm emission, outer disk	a dozen of disks (0.9 − 4.4) × 1012 cm−2	(27,28,29,30,33,41,43,44) (33)c	a handful of disks (1.6 − 3.3) × 1012 cm−2	(30,33,34,42,45,46) (33)d
CH3OH	mm emission (ALMA), outer disk	one disk: TW Hya; (3 − 6) × 1012 cm−2	(47)	none
HC3N	mm emission, outer disk	two disks: GO Tau, LkCa 15; ~ 1012 cm−2	(48)	one disk: MWC 480; ~ 1012 cm−2	(48,49)
CH3CN	mm emission (ALMA), outer disk	none		one disk: MWC 480; ~ 1013 cm−2	(49)
c-C3H2	mm emission (ALMA), outer disk	one disk: TW Hya	(38)	one disk: HD 163296; 1012 − 1013 cm−2	(50)
NH3	sub-mm emission, outer disk	one disk: TW Hya (0.2 − 17) × 10−11 relative to H2	(51) (51)	none
CS	mm emission, outer disk	a dozen of disks (1 − 20.9) × 1012 cm−2	(27,32,33,52) (32,33,52)	two disks: AB Aur, MWC 480 (0.4 − 6.3) × 1012cm−2	(33,34,40) (33,34)
SO	mm emission, outer disk	two disks: CI Tau, GM Aur (7.4 − 9) × 1012 cm−2	(33) (33)	one disk: AB Aur (0.5 − 10) × 1012 cm−2	(33,34,40,42) (33,34,42)
HCO+	mm emission, outer disk	many disks (0.3 − 20) × 1012 cm−2	(28,29,30,33,35,53,54,55) (28,33,53,54,55)	many disks (0.2 − 5) × 1012 cm−2	(28,29,30,33,34,54,56) (28,33,34,54)e
N2H+	mm emission, outer disk	a handful of disks (0.1 − 30) × 1012 cm−2	(29,30,44,53,54,57) (53,54)f	one disk: HD 163296 1.7 × 1011 cm−2	(45) (45)
CH+	sub-mm emission, mid disk	none		two disks: HD 100546, HD 97048 4.3 × 1012 cm−2	(15,58) (58)g

References: (1) Carr et al. (2004); (2) Carr & Najita (2008); (3) Salyk et al. (2008); (4) Pontoppidan et al. (2010a); (5) Pontoppidan et al. (2010b); (6) Carr & Najita (2011); (7) Salyk et al. (2011); (8) Mandell et al. (2012); (9) Riviere-Marichalar et al. (2012); (10) Sargent et al. (2014); (11) Banzatti et al. (2017); (12) Fedele et al. (2011); (13) Meeus et al. (2012); (14) Fedele et al. (2012); (15) Fedele et al. (2013); (16) Hogerheijde et al. (2011); (17) Podio et al. (2013); (18) Du et al. (2017); (19) van Dishoeck et al. (2014); (20) Carr & Najita (2014); (21) Mandell et al. (2008); (22) Lahuis et al. (2006); (23) Gibb et al. (2007); (24) Bast et al. (2013); (25) Gibb & Horne (2013); (26) Kruger et al. (2011); (27) Dutrey et al. (1997); (28) Thi et al. (2004); (29) Öberg et al. (2010); (30) Öberg et al. (2011); (31) Chapillon et al. (2012a); (32) Kastner et al. (2014); (33) Guilloteau et al. (2016); (34) Fuente et al. (2010); (35) Fuente et al. (2012); (36) Graninger et al. (2015); (37) Henning et al. (2010); (38) Bergin et al. (2016); (39) Schreyer et al. (2008); (40) Pacheco-Vázquez et al. (2015); (41) Aikawa et al. (2003); (42) Pacheco-Vázquez et al. (2016); (43) Loomis et al. (2015); (44) Öberg et al. (2017); (45) Qi et al. (2013a); (46) Carney et al. (2017); (47) Walsh et al. (2016); (48) Chapillon et al. (2012b); (49) Öberg et al. (2015); (50) Qi et al. (2013b); (51) Salinas et al. (2016); (52) Dutrey et al. (2011); (53) Qi et al. (2003); (54) Dutrey et al. (2007); (55) Teague et al. (2015); (56) Mathews et al. (2013); (57) Qi et al. (2013c); (58) Thi et al. (2011).

Notes:

^aValues are line intensity ratios rather than abundance ratios.

^bOut of this range, Kastner et al. (2014) derive N(C₂H) = 5.1 × 10¹⁵ cm⁻² in TW Hya.

^cOut of this range, Aikawa et al. (2003) derive N(H₂CO) = (7.2 − 19) × 10¹² cm⁻² in LkCa 15.

^dCarney et al. (2017) derive a H₂CO abundance of (2 − 5) × 10^-12 relative to H₂ in HD 163296.

^eOut of this range, Mathews et al. (2013) derive N(HCO⁺) = 1.5 × 10¹⁴ cm⁻² in HD 163296.

^fOut of this range, Qi et al. (2013c) derive N(N₂H+) = 10¹⁴ − 10¹⁵ cm⁻² in TW Hya.

^gIn the same object, HD 100546, Fedele et al. (2013) derive N(CH⁺) = 10¹⁶ − 10¹⁷ cm⁻² for an emitting area inner to 50-70 au.