The influence of excited-state vibrations on fragment state distributions: The photodissociation of NOCl on T1(1 3A'')

Article abstract of DOI:10.1063/1.457789

NO V,R distributions are reported following photodissociation of jet-cooled NOCl from selected vibrational levels of the T₁(1³A'') state.By varying the photolysis wavelength while monitoring selected rovibrational levels of NO, a photofragment yield spectrum showing the same diffuse vibrational structure as the absorbtion spectrum is obtained.NO rotational distributions are obtained at photolysis wavelengths corresponding to peaks in the absorption spectrum.We find that the NO stretching vibrations of T₁ evolve adiabatically into NO vibrational excitations 1 quanta of the T₁ NO stretch yields predominantly NO(υ''= υ₁)>.The NO rotational distributions depend only on the number of T₁ bending quanta, υ₃.The shapes of the distributions reflect the number of nodes in the bending wave functions, and similar rotational distributions are obtained following excitation of vibronic levels with equal number of ν₃ quanta, but different number of ν₁ quanta (υ₁ = 0-2).We also find that the excited NO(²Π_3/2) state is much more populated than the lower NO(²Π_1/2) state, and the widths of the absorbtion features increase with increasing number of ν₃ quanta, but decrease with increasing ν₁ excitation.The results are explained in terms of a model in which the bending and NO stretch motions in the excited state are largely uncoupled.In order to explain the multimodal rotational distributions, we calculate separately the components of the NO rotational excitation that derive from the angular momentum inherent in the bending wave function and the angular anisotropy in the potentail-energy surface.We find, using the momentum representation of the harmonic oscillator, that the rotational distributions map the bending wave functions and exhibit minima for υ₃>0.In addition, a unidirectional torque generated by the angular anisotropy in the potential causes shifts in the distributions calculated by the pure Franck-Condon model that are bending level dependent.The observation that the absorption linewidth decreases with increasing NO stretch excitation in the parent T₁ state may be a manifestation of the energy mismatch between the frequency of the NO stretch in NOCl and free NO; the increased mismatch with increasing stretch quantum number results in slower dissociation.

Full text of DOI:10.1063/1.457789

The influence of excitedstate vibrations on fragment state distributions: The
photodissociation of NOCl on T1(13A‘)
C. X. W. Qian, A. Ogai, L. Iwata, and H. Reisler
Citation: The Journal of Chemical Physics 92, 4296 (1990); doi: 10.1063/1.457789
View online: http://dx.doi.org/10.1063/1.457789
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/92/7?ver=pdfcov
Published by the AIP Publishing
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