Photofragment imaging of HNCO decomposition: Angular anisotropy and correlated distributions

Journal Article · Thu May 01 04:00:00 EDT 1997 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.473724· OSTI ID:554232

Sanov, A; Droz-Georget, T; Zyrianov, M; Reisler, H ^[1]

---

1. Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482 (United States)

Photodissociation of jet-cooled isocyanic acid has been examined by photofragment ion imaging of H(D) from H(D)NCO and CO from HNCO, and by laser induced fluorescence (LIF) of NH(a{sup 1}{Delta}) from HNCO. Only modest recoil anisotropy is observed in the H+NCO channel at 243.1 nm ({beta}={minus}0.13{plus_minus}0.05), while the D+NCO channel at approximately the same wavelength reveals no anisotropy ({beta}=0.00{plus_minus}0.05), confirming that the dissociation of H(D)NCO from the opening of the H(D) channel proceeds via vibrational predissociation on the S{sub 0}({sup 1}A) surface. In contrast, substantial anisotropy ({beta}={minus}0.66{plus_minus}0.08) is observed in the NH(a{sup 1}{Delta})+CO channel at 230.1 nm, but this value can correspond to dissociation on either S{sub 0} or S{sub 1}. The photolysis region between 243 and 230 nm thus appears important in providing clues to the dissociation mechanism and the competition between different potential energy surfaces. At 217.6 nm, product state distributions exhibit clear dynamical biases. CO is produced in both {nu}=0 and {nu}=1, while NH(a{sup 1}{Delta}) distributions correlated with different rovibrational levels of CO, although different in shape, are always cold, consistent with the global NH distribution measured by LIF. The NH distributions indicate dissociation on S{sub 1}({sup 1}A{sup {prime}{prime}}), and can be described by Franck{endash}Condon mapping of transition state wave functions in the HNC bending coordinate without additional torque, implying little anisotropy in the potential along that coordinate. On the other hand, a larger torque is manifest in the CO rotational distribution. Although at 217.6 nm the dissociation is likely to be dominated by decomposition on S{sub 1}, competition with radiationless decay is still manifest. The NH(a{sup 1}{Delta})+CO dissociation threshold is determined at 42765{plus_minus}25cm{sup {minus}1}. {copyright} {ital 1997 American Institute of Physics.}

• OSTI ID: 554232
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 17 Vol. 106; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ANGULAR DISTRIBUTION
ANISOTROPY
CARBON MONOXIDE
CYANIDES
DECOMPOSITION
DEUTERIUM COMPOUNDS
FLUORESCENCE
FLUORESCENCE SPECTROSCOPY
HYDROCYANIC ACID
HYDROGEN COMPOUNDS
ISOCYANIC ACID ESTERS
ISOTOPE EFFECTS
LASER SPECTROSCOPY
NITROGEN HYDRIDES
OXYGEN COMPOUNDS
PHOTON-MOLECULE COLLISIONS
POTENTIAL ENERGY
PREDISSOCIATION