Kinetics and Dynamics on the Formation of S2(X3危g鈥?/sup>,a1螖g) in the S(1D) + OCS Reaction

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• 作者：Jun Yamashita ; Keigo Fujihara ; Osamu Takahashi ; Hiroshi Kohguchi ; Katsuyoshi Yamasaki
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：October 9, 2014
• 年：2014
• 卷：118
• 期：40
• 页码：9330-9337
• 全文大小：398K
• ISSN：1520-5215

文摘

The reaction of electronically excited sulfur S(¹D) with OCS has exothermic channels generating S₂ in two electronic states X³危_g^{鈥?/sup> and a1螖_g. The a1螖_g state is correlated directly to the reactants via the spin-allowed singlet surface; the X3危_g鈥?/sup> state, on the other hand, is a product of the spin-forbidden channel. There has been no report on kinetic evidence for the simultaneous generation of the two electronic states, although the two electronic states have been detected so far. The previous studies showed that little energy was released into rotation or vibration of the S₂ products despite large heats of reactions (228 and 175 kJ mol鈥? for generation of X3危_g鈥?/sup> and a1螖_g, respectively). In the present study, S(1D) was generated by the photolysis of OCS at 248 nm in a buffer He at 298 K, and the resulting two electronic states of S₂ (X3危_g鈥?/sup> and a1螖_g) were detected with dispersed laser-induced fluorescence (LIF) via the B3危_u鈥?/sup>鈥揦3危_g鈥?/sup> and f1螖_u鈥揳1螖_g transitions, respectively. Not only excitation but also dispersed fluorescence spectra made it possible to find a single rotational line of the vibrational level of interest. The time-resolved LIF intensities of the initial growth of the X3危_g鈥?/sup> and a1螖_g states showed identical OCS pressure dependences, giving the overall rate coefficient of the S(1D) + OCS reaction to be [3.2 卤 0.2(2蟽)] 脳 10鈥?0 cm3 molecule鈥? s鈥?. The simultaneous generation of the two electronic states indicates that the intersystem crossing plays a role in opening the spin-forbidden channel. As for the reaction dynamics, vibrational levels up to v = 19 of X3危_g鈥?/sup> and 11 of a1螖_g have been detected, which is distinctly different from the previous studies. The reaction mechanism has been discussed on the basis of the potential energies reported so far.}