Photoinitiated decomposition of HNCO near the H+NCO threshold: Centrifugal barriers and channel competition

M. Zyrianov, Andrei M Sanov, Th Droz-Georget, H. Reisler

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The decomposition of jet-cooled HNCO is investigated near the H+NCO channel threshold [D0(H+NCO)=38 370 cm-1]. Dissociation to H+NCO at energies 17-411 cm-1 above D0(H+NCO) proceeds on the ground potential energy surface (S0), apparently without a barrier. The rotational state distributions of the NCO(X2Π3/2,0010) fragment are well described by phase space theory (PST), provided that dynamical constraints are included. These constraints are associated with long range (4-7 Å) centrifugal barriers, which are significant even near threshold because of the small reduced mass of H+NCO, and result in a fraction of energy deposited in fragment rotation much smaller than predicted by unconstrained PST. The influence of orientation averaging on the attractive, long-range part of the potential is discussed, and it is argued that angular averaging with respect to the center of mass of the rotating polyatomic fragment results in a shift in the effective potential origin, accompanied by an attenuation of the magnitude of the potential compared to its value for fixed H-N distance. Following initial S1(1A″)←S0(1A′) excitation and internal conversion to S0, HNCO(S0) decays both via unimolecular decomposition of H+NCO and intersystem crossing to the dissociative first triplet state, T1 [yielding NH(X3-)+ CO products]. The competition between the two processes is interrogated by monitoring changes in the relative yields of NCO and NH(X3-) as a function of excitation energy. It is concluded that near D0(H+NCO), the S0→T1 intersystem crossing rate is several-fold faster than the H+NCO unimolecular decomposition rate.

Original languageEnglish (US)
Pages (from-to)10774-10783
Number of pages10
JournalThe Journal of Chemical Physics
Volume110
Issue number22
StatePublished - Jun 8 1999
Externally publishedYes

Fingerprint

fragments
Decomposition
decomposition
thresholds
Potential energy surfaces
Excitation energy
internal conversion
rotational states
Carbon Monoxide
atomic energy levels
excitation
center of mass
energy
attenuation
potential energy
dissociation
Monitoring
shift
decay
products

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Photoinitiated decomposition of HNCO near the H+NCO threshold : Centrifugal barriers and channel competition. / Zyrianov, M.; Sanov, Andrei M; Droz-Georget, Th; Reisler, H.

In: The Journal of Chemical Physics, Vol. 110, No. 22, 08.06.1999, p. 10774-10783.

Research output: Contribution to journalArticle

@article{0a7e6d0ffa684932a43e6a5ca950839e,
title = "Photoinitiated decomposition of HNCO near the H+NCO threshold: Centrifugal barriers and channel competition",
abstract = "The decomposition of jet-cooled HNCO is investigated near the H+NCO channel threshold [D0(H+NCO)=38 370 cm-1]. Dissociation to H+NCO at energies 17-411 cm-1 above D0(H+NCO) proceeds on the ground potential energy surface (S0), apparently without a barrier. The rotational state distributions of the NCO(X2Π3/2,0010) fragment are well described by phase space theory (PST), provided that dynamical constraints are included. These constraints are associated with long range (4-7 {\AA}) centrifugal barriers, which are significant even near threshold because of the small reduced mass of H+NCO, and result in a fraction of energy deposited in fragment rotation much smaller than predicted by unconstrained PST. The influence of orientation averaging on the attractive, long-range part of the potential is discussed, and it is argued that angular averaging with respect to the center of mass of the rotating polyatomic fragment results in a shift in the effective potential origin, accompanied by an attenuation of the magnitude of the potential compared to its value for fixed H-N distance. Following initial S1(1A″)←S0(1A′) excitation and internal conversion to S0, HNCO(S0) decays both via unimolecular decomposition of H+NCO and intersystem crossing to the dissociative first triplet state, T1 [yielding NH(X3∑-)+ CO products]. The competition between the two processes is interrogated by monitoring changes in the relative yields of NCO and NH(X3∑-) as a function of excitation energy. It is concluded that near D0(H+NCO), the S0→T1 intersystem crossing rate is several-fold faster than the H+NCO unimolecular decomposition rate.",
author = "M. Zyrianov and Sanov, {Andrei M} and Th Droz-Georget and H. Reisler",
year = "1999",
month = "6",
day = "8",
language = "English (US)",
volume = "110",
pages = "10774--10783",
journal = "Journal of Chemical Physics",
issn = "0021-9606",
publisher = "American Institute of Physics Publising LLC",
number = "22",

}

TY - JOUR

T1 - Photoinitiated decomposition of HNCO near the H+NCO threshold

T2 - Centrifugal barriers and channel competition

AU - Zyrianov, M.

AU - Sanov, Andrei M

AU - Droz-Georget, Th

AU - Reisler, H.

PY - 1999/6/8

Y1 - 1999/6/8

N2 - The decomposition of jet-cooled HNCO is investigated near the H+NCO channel threshold [D0(H+NCO)=38 370 cm-1]. Dissociation to H+NCO at energies 17-411 cm-1 above D0(H+NCO) proceeds on the ground potential energy surface (S0), apparently without a barrier. The rotational state distributions of the NCO(X2Π3/2,0010) fragment are well described by phase space theory (PST), provided that dynamical constraints are included. These constraints are associated with long range (4-7 Å) centrifugal barriers, which are significant even near threshold because of the small reduced mass of H+NCO, and result in a fraction of energy deposited in fragment rotation much smaller than predicted by unconstrained PST. The influence of orientation averaging on the attractive, long-range part of the potential is discussed, and it is argued that angular averaging with respect to the center of mass of the rotating polyatomic fragment results in a shift in the effective potential origin, accompanied by an attenuation of the magnitude of the potential compared to its value for fixed H-N distance. Following initial S1(1A″)←S0(1A′) excitation and internal conversion to S0, HNCO(S0) decays both via unimolecular decomposition of H+NCO and intersystem crossing to the dissociative first triplet state, T1 [yielding NH(X3∑-)+ CO products]. The competition between the two processes is interrogated by monitoring changes in the relative yields of NCO and NH(X3∑-) as a function of excitation energy. It is concluded that near D0(H+NCO), the S0→T1 intersystem crossing rate is several-fold faster than the H+NCO unimolecular decomposition rate.

AB - The decomposition of jet-cooled HNCO is investigated near the H+NCO channel threshold [D0(H+NCO)=38 370 cm-1]. Dissociation to H+NCO at energies 17-411 cm-1 above D0(H+NCO) proceeds on the ground potential energy surface (S0), apparently without a barrier. The rotational state distributions of the NCO(X2Π3/2,0010) fragment are well described by phase space theory (PST), provided that dynamical constraints are included. These constraints are associated with long range (4-7 Å) centrifugal barriers, which are significant even near threshold because of the small reduced mass of H+NCO, and result in a fraction of energy deposited in fragment rotation much smaller than predicted by unconstrained PST. The influence of orientation averaging on the attractive, long-range part of the potential is discussed, and it is argued that angular averaging with respect to the center of mass of the rotating polyatomic fragment results in a shift in the effective potential origin, accompanied by an attenuation of the magnitude of the potential compared to its value for fixed H-N distance. Following initial S1(1A″)←S0(1A′) excitation and internal conversion to S0, HNCO(S0) decays both via unimolecular decomposition of H+NCO and intersystem crossing to the dissociative first triplet state, T1 [yielding NH(X3∑-)+ CO products]. The competition between the two processes is interrogated by monitoring changes in the relative yields of NCO and NH(X3∑-) as a function of excitation energy. It is concluded that near D0(H+NCO), the S0→T1 intersystem crossing rate is several-fold faster than the H+NCO unimolecular decomposition rate.

UR - http://www.scopus.com/inward/record.url?scp=0001339771&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0001339771&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0001339771

VL - 110

SP - 10774

EP - 10783

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 22

ER -