Photodissociation and photoionization of organosulfur radicals

Hsu, Chia-Wei
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The dynamics of S([superscript]3P[subscript]2,1,0,[superscript]1D[subscript]2) production from the 193 nm photodissociation of CH[subscript]3SCH[subscript]3, H[subscript]2S and CH[subscript]3SH have been studied using 2+1 resonance-enhanced multiphoton ionization (REMPI) techniques. The 193 nm photodissociation cross sections for the formation of S from CH[subscript]3S and H[subscript]2S initially prepared in the photodissociation of CH[subscript]3SCH[subscript]3 and H[subscript]2S are estimated to be 1x 10[superscript]-18 and 1.1x 10[superscript]-18 cm[superscript]2, respectively. The dominant product from CH[subscript]3S is S([superscript]1D), while that from SH is S([superscript]3P). Possible potential energy surfaces involved in the 193 nm photodissociation of CH[subscript]3S(~ X) and SH(X) have been also examined theoretically. Threshold photoelectron (PE) spectra for SH and CH[subscript]3S formed in the ultraviolet photodissociation of H[subscript]2S and CH[subscript]3SH, respectively, have been measured using the nonresonant two-photon pulsed field ionization (N2P-PFI) technique. The rotationally resolved N2P-PFI-PE spectrum obtained for SH indicates that photoionization dynamics favors the rotational angular momentum change [delta] N < 0 with the [delta] N value up to -3, an observation similar to that found in the PFI-PE spectra of OH (OD) and NO. The ionization energies for SH(X[superscript]2[pi][subscript]3/2) and CH[subscript]3S(~ X[superscript]2E[subscript]3/2) are determined to be 84,057.5 ± 3 cm[superscript]-1 (10.4219 ± 0.0004 eV) and 74,726 ± 8 cm[superscript]-1 (9.2649 ± 0.0010 eV), respectively. The spin-orbit splittings for SH(X[superscript]2[pi][subscript]3/2,1/2) and CH[subscript]3S(~ X[superscript]2E[subscript]3/2,1/2) are found to be 377 ± 2 and 257 ± 5 cm[superscript]-1, respectively, in agreement with previous measurements. The C-S stretching frequency for CH[subscript]3S[superscript]+(~ X[superscript]3A[subscript]2) is 733 ± 5 cm[superscript]-1. This study illustrates that the PFI-PE detection method can be a sensitive probe for the nascent internal energy distribution of photoproducts.

Chemistry, Physical chemistry