Importance of intersystem crossing in the S( 3P, 1D) + H 2 → SH + H reaction

Biswajit Maiti, George C. Schatz, György Lendvay

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Abstract

A "mixed" representation approach in conjunction with a trajectory surface-hopping method is used to study intersystem crossing effects in the S + H 2 reaction. These calculations are based on high-quality potential surfaces that we have determined for the two lowest triplet states of SH 2 and globally determined spin-orbit coupling matrix elements that are obtained from CASSCF calculations. A previously determined surface for the lowest singlet state (Ho, T.-S.; Hollebeek, T.; Rabitz, H.; Chao, S. D.; Skodje, R. T.; Zyubin, A. S.; Mebel, A. M. J. Chem. Phys. 2002, 116, 4124) is also used. We find that in contrast to the O( 3P) + H 2 reaction, which we studied previously at the same level, there is significant intersystem crossing in the S( 3P) + H 2 reaction. In particular, for the reaction starting from triplet S + H 2 close to the threshold, the dominant mechanism involves intersystem crossing to the singlet state prior to encountering the triplet barrier, and as a result, the thermal rate constant at low temperatures is controlled by intersystem crossing. This behavior occurs in part because the spin-orbit coupling is about 3 times larger in S than in O, but another important factor is the location of the singlet/triplet crossing, which occurs on the reagent side of the triplet barrier in S + H 2 and on the product side in O + H 2. We also find that trajectories that undergo a triplet-to-singlet transition have higher product rotational excitation than those that remain on the triplet surfaces. For the S( 1D) + H 2 reaction, we find significant electronic quenching due to intersystem crossing, leading to a factor of 2 or more reduction in the reactive cross section, and a much flatter dependence of the cross section on collision energy for energies above 2.5 kcal/mol. This result agrees with recent molecular beam measurements.

Original languageEnglish
Pages (from-to)8772-8781
Number of pages10
JournalJournal of Physical Chemistry A
Volume108
Issue number41
DOIs
Publication statusPublished - Oct 14 2004

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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