Isocyanic acid

Formula: CHNO
Molecular weight: 43.0247
IUPAC Standard InChI: InChI=1S/CHNO/c2-1-3/h2H
IUPAC Standard InChIKey: OWIKHYCFFJSOEH-UHFFFAOYSA-N
CAS Registry Number: 75-13-8
Chemical structure:
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Other data available:
- Gas phase thermochemistry data
- Gas phase ion energetics data
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Reaction thermochemistry data

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Individual Reactions

CNO^- + = Isocyanic acid

By formula: CNO^- + H⁺ = CHNO

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1427.5 ± 2.6	kJ/mol	D-EA	Bradforth, Kim, et al., 1993	gas phase; D-EA cycle requires a DH ca 4 kcal/mol weaker
Δ_rH°	1442. ± 8.8	kJ/mol	G+TS	Wight and Beauchamp, 1980	gas phase
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1400.6 ± 3.0	kJ/mol	H-TS	Bradforth, Kim, et al., 1993	gas phase; D-EA cycle requires a DH ca 4 kcal/mol weaker
Δ_rG°	1415. ± 8.4	kJ/mol	IMRE	Wight and Beauchamp, 1980	gas phase

(CAS Reg. No. 1140500-24-8 • 4294967295 Isocyanic acid ) + = CAS Reg. No. 1140500-24-8

By formula: (CAS Reg. No. 1140500-24-8 • 4294967295CHNO) + CHNO = CAS Reg. No. 1140500-24-8

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	180. ± 13.	kJ/mol	N/A	Taft, 1987	gas phase; value altered from reference due to change in acidity scale

(CAS Reg. No. 67131-48-0 • 4294967295 Isocyanic acid ) + = CAS Reg. No. 67131-48-0

By formula: (CAS Reg. No. 67131-48-0 • 4294967295CHNO) + CHNO = CAS Reg. No. 67131-48-0

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	243. ± 9.2	kJ/mol	N/A	Taft, 1987	gas phase; value altered from reference due to change in acidity scale

Vibrational and/or electronic energy levels

Go To: Top, Reaction thermochemistry data, References, Notes

Data compiled as indicated in comments:
J - Marilyn E. Jacox
Shim - Takehiko Shimanouchi

State: ?

Energy (cm^-1)	Med.	λ_min (nm)	λ_max (nm)	References


T_d	gas	120	133	Okabe, 1970

State: ?

Energy (cm^-1)	Med.	λ_min (nm)	λ_max (nm)	References


72940	gas	134	137	Okabe, 1970

State: ?

Energy (cm^-1)	Med.	λ_min (nm)	λ_max (nm)	References


T_d	gas	147	163	Okabe, 1970

State: ?

Energy (cm^-1)	Med.	λ_min (nm)	λ_max (nm)	References


T_d	gas	163	185	Okabe, 1970

State: ?

Energy (cm^-1)	Med.	λ_min (nm)	λ_max (nm)	References


T_d = 41000	gas	200U	244	Dixon and Kirby, 1968

State: A

Energy (cm^-1)	Med.	Transition	λ_min (nm)	λ_max (nm)	References


T_o = 32449 ± 20	gas	A-X	228	282	Dixon and Kirby, 1968
					Berghout, Crim, et al., 2000

Vib. sym.	No.	Approximate type of mode	cm^-1	Med.	Method	References


a'	3	HNC bend	1192 ± 10	gas	PF	Berghout, Crim, et al., 2000
	4	NC stretch	1034 ± 20	gas	PF	Berghout, Crim, et al., 2000
	5	NCO bend	599 ± 7	gas	PF	Berghout, Crim, et al., 2000

State: X

Vib. sym.	No.	Approximate type of mode	cm^-1		Med.	Method	References


a'	1	NH stretch	3538.24	s	gas	IR Ra	Herzberg and Reid, 1950 Reid, 1950 Teles, Maier, et al., 1989 Yamada, Winnewisser, et al., 1990 Brown, Berghout, et al., 1997
	1	NH stretch	3516.8	w m	Ar	IR	Teles, Maier, et al., 1989
	1	NH stretch	3505.7	w m	Ar	IR	Teles, Maier, et al., 1989
	1	NH stretch	3514.7		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	1	NH stretch	3500.6		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	1	NH stretch	3485.2		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	1	NH stretch	3483.0		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	1	NH stretch	3479.9		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	2	NCO a-stretch	2268.89	vs	gas	IR	Herzberg and Reid, 1950 Reid, 1950 Lemoine, Yamada, et al., 1982 Steiner, Polo, et al., 1983 Brown, Berghout, et al., 1997, 2
	2	NCO a-stretch	2259.0	vs	Ar	IR	Teles, Maier, et al., 1989 Crowley and Sodeau, 1989
	2	NCO a-stretch	2261.6		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	2	NCO a-stretch	2254.4		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	3	NCO s-stretch	1327	w	gas	IR	Herzberg and Reid, 1950 Reid, 1950 Brown, Berghout, et al., 1997, 2
	4	HNC, NCO bend	776.62	w m	gas	IR	Steiner, Wishah, et al., 1979
	4	HNC, NCO bend	769.8	w m	Ar	IR	Teles, Maier, et al., 1989 Crowley and Sodeau, 1989
	4	HNC, NCO bend	763.6		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	4	HNC, NCO bend	765.1		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	4	HNC, NCO bend	760.3		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	5	HNC, NCO bend	577.35	w	gas	IR	Herzberg and Reid, 1950 Reid, 1950 Steiner, Wishah, et al., 1979
	5	HNC, NCO bend	573.7	w m	Ar	IR	Teles, Maier, et al., 1989 Crowley and Sodeau, 1989
	5	HNC, NCO bend	572.9		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	5	HNC, NCO bend	571.3		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	5	HNC, NCO bend	574.2		Xe	IR	Pettersson, Khriachtchev, et al., 1999
	5	HNC, NCO bend	570.3		Xe	IR	Pettersson, Khriachtchev, et al., 1999
a	6	Torsion	656.29		gas	IR	Steiner, Wishah, et al., 1979 Fusina, Carlotti, et al., 1984
	6	Torsion (1-0)	695.6		Kr	IR	Pettersson, Khriachtchev, et al., 1999
	6	Torsion (1-0)	694.7		Xe	IR	Pettersson, Khriachtchev, et al., 1999

Additional references: Jacox, 1994, page 163; Jacox, 1998, page 236; Jacox, 2003, page 190; Ashby and Werner, 1966; Yamada, 1980; Steiner, Polo, et al., 1981

Notes

Weak

Medium

Strong

Very strong

Energy separation between the v = 0 levels of the excited and electronic ground states.

Photodissociation threshold

References

Go To: Top, Reaction thermochemistry data, Vibrational and/or electronic energy levels, Notes

Bradforth, Kim, et al., 1993
Bradforth, S.E.; Kim, E.H.; Arnold, D.W.; Neumark, D.M., Photoelectron Spectroscopy of CN-, NCO-, and NCS-, J. Chem. Phys., 1993, 98, 2, 800, https://doi.org/10.1063/1.464244 . [all data]

Wight and Beauchamp, 1980
Wight, C.A.; Beauchamp, J.L., Acidity, basicity, and ion/molecule reactions of isocyanic acid in the gas phase by ICR spectroscopy, J. Phys. Chem., 1980, 84, 2503. [all data]

Taft, 1987
Taft, R.W., The Nature and Analysis of Substitutent Electronic Effects, Personal communication. See also Prog. Phys. Org. Chem., 1987, 16, 1. [all data]

Okabe, 1970
Okabe, H., J. Chem. Phys., 1970, 53, 3507. [all data]

Dixon and Kirby, 1968
Dixon, R.N.; Kirby, G.H., Ultra-violet absorption spectrum of isocyanic acid, Trans. Faraday Soc., 1968, 64, 2002, https://doi.org/10.1039/tf9686402002 . [all data]

Berghout, Crim, et al., 2000
Berghout, H.L.; Crim, F.F.; Zyrianov, M.; Reisler, H., The electronic origin and vibrational levels of the first excited singlet state of isocyanic acid (HNCO), J. Chem. Phys., 2000, 112, 15, 6678, https://doi.org/10.1063/1.481242 . [all data]

Herzberg and Reid, 1950
Herzberg, G.; Reid, C., Infra-red spectrum and structure of the HNCO molecule, Discuss. Faraday Soc., 1950, 9, 92, https://doi.org/10.1039/df9500900092 . [all data]

Reid, 1950
Reid, C., Rotation-Vibration Spectra of Diatomic and Simple Polyatomic Molecules with Long Absorbing Paths V. The Spectrum of Isocyanic Acid, J. Chem. Phys., 1950, 18, 12, 1544, https://doi.org/10.1063/1.1747538 . [all data]

Teles, Maier, et al., 1989
Teles, J.H.; Maier, G.; Hess, B.A., Jr.; Schaad, L.J.; Winnewisser, M.; Winnewisser, B.P., The CHNO Isomers, Chem. Ber., 1989, 122, 4, 753, https://doi.org/10.1002/cber.19891220425 . [all data]

Yamada, Winnewisser, et al., 1990
Yamada, K.M.T.; Winnewisser, M.; Johns, J.W.C., High-resolution spectrum of the ν1 fundamental band of isocyanic acid, HNCO, J. Mol. Spectrosc., 1990, 140, 2, 353, https://doi.org/10.1016/0022-2852(90)90147-I . [all data]

Brown, Berghout, et al., 1997
Brown, S.S.; Berghout, H.L.; Crim, F.F., Raman spectroscopy of the ν1 N--H stretch fundamental in isocyanic acid (HNCO): State mixing probed by photoacoustic spectroscopy and by photodissociation of vibrationally excited states, J. Chem. Phys., 1997, 106, 14, 5805, https://doi.org/10.1063/1.473246 . [all data]

Pettersson, Khriachtchev, et al., 1999
Pettersson, M.; Khriachtchev, L.; Jolkkonen, S.; Rasanen, M., Photochemistry of HNCO in Solid Xe: Channels of UV Photolysis and Creation of H, J. Phys. Chem. A, 1999, 103, 45, 9154, https://doi.org/10.1021/jp992224d . [all data]

Lemoine, Yamada, et al., 1982
Lemoine, B.; Yamada, K.; Winnewisser, G., Diode Laser Spectrum of the Fundamental v2 Band of HNCO, Ber. Bunsenges. Phys. Chem., 1982, 86, 9, 795, https://doi.org/10.1002/bbpc.19820860906 . [all data]

Steiner, Polo, et al., 1983
Steiner, D.A.; Polo, S.R.; McCubbin, T.K.; Wishah, K.A., Infrared spectrum of the fundamental ν2 of isocyanic acid, J. Mol. Spectrosc., 1983, 98, 2, 453, https://doi.org/10.1016/0022-2852(83)90254-0 . [all data]

Brown, Berghout, et al., 1997, 2
Brown, S.S.; Berghout, H.L.; Crim, F.F., Raman spectroscopy of the N--C--O symmetric (ν[sub 3]) and antisymmetric (ν[sub 2]) stretch fundamentals in HNCO, J. Chem. Phys., 1997, 107, 23, 9764, https://doi.org/10.1063/1.475274 . [all data]

Crowley and Sodeau, 1989
Crowley, J.N.; Sodeau, J.R., Reaction between hydrocyanic acid and O(1D2) or O(3P) oxygen atoms in low-temperature matrixes, J. Phys. Chem., 1989, 93, 8, 3100, https://doi.org/10.1021/j100345a044 . [all data]

Steiner, Wishah, et al., 1979
Steiner, D.A.; Wishah, K.A.; Polo, S.R.; McCubbin, T.K., Infrared spectrum of isocyanic acid between 465 and 1100 cm-1, J. Mol. Spectrosc., 1979, 76, 1-3, 341, https://doi.org/10.1016/0022-2852(79)90233-9 . [all data]

Fusina, Carlotti, et al., 1984
Fusina, L.; Carlotti, M.; Carli, B., Infrared spectrum of HNCO between 8 and 80 cm, Can. J. Phys., 1984, 62, 12, 1452, https://doi.org/10.1139/p84-192 . [all data]

Jacox, 1994
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules, American Chemical Society, Washington, DC, 1994, 464. [all data]

Jacox, 1998
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules: supplement A, J. Phys. Chem. Ref. Data, 1998, 27, 2, 115-393, https://doi.org/10.1063/1.556017 . [all data]

Jacox, 2003
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules: supplement B, J. Phys. Chem. Ref. Data, 2003, 32, 1, 1-441, https://doi.org/10.1063/1.1497629 . [all data]

Ashby and Werner, 1966
Ashby, R.A.; Werner, R.L., The infra-red absorption spectrum of DNCO, Spectrochim. Acta, 1966, 22, 7, 1345, https://doi.org/10.1016/0371-1951(66)80038-3 . [all data]

Yamada, 1980
Yamada, K., Molecular structure and centrifugal distortion constants of isocyanic acid from the microwave, millimeter wave, and far-infrared spectra, J. Mol. Spectrosc., 1980, 79, 2, 323, https://doi.org/10.1016/0022-2852(80)90217-9 . [all data]

Steiner, Polo, et al., 1981
Steiner, D.A.; Polo, S.R.; McCubbin, T.K.; Wishah, K.A., Infrared spectrum of the fundamental ν, Can. J. Phys., 1981, 59, 10, 1313, https://doi.org/10.1139/p81-172 . [all data]

Notes

Go To: Top, Reaction thermochemistry data, Vibrational and/or electronic energy levels, References

Symbols used in this document:

Δ_rG° Free energy of reaction at standard conditions

Δ_rH° Enthalpy of reaction at standard conditions
Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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Δ_rG°	Free energy of reaction at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions