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Title: Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: Intramolecular orbital alignment of the phenylthiyl radical

Abstract

The photoinduced hydrogen (or deuterium) detachment reaction of thiophenol (C{sub 6}H{sub 5}SH) or thiophenol-d{sub 1} (C{sub 6}H{sub 5}SD) pumped at 243 nm has been investigated using the H (D) ion velocity map imaging technique. Photodissociation products, corresponding to the two distinct and anisotropic rings observed in the H (or D) ion images, are identified as the two lowest electronic states of phenylthiyl radical (C{sub 6}H{sub 5}S{center_dot}). Ab initio calculations show that the singly occupied molecular orbital of the phenylthiyl radical is localized on the sulfur atom and it is oriented either perpendicular or parallel to the molecular plane for the ground (B{sub 1}) and the first excited state (B{sub 2}) species, respectively. The experimental energy separation between these two states is 2600{+-}200 cm{sup -1} in excellent agreement with the authors' theoretical prediction of 2674 cm{sup -1} at the CASPT2 level. The experimental anisotropy parameter ({beta}) of -1.0{+-}0.05 at the large translational energy of D from the C{sub 6}H{sub 5}SD dissociation indicates that the transition dipole moment associated with this optical transition at 243 nm is perpendicular to the dissociating S-D bond, which in turn suggests an ultrafast D+C{sub 6}H{sub 5}S{center_dot}(B{sub 1}) dissociation channel on a repulsive potential energy surface. Themore » reduced anisotropy parameter of -0.76{+-}0.04 observed at the smaller translational energy of D suggests that the D+C{sub 6}H{sub 5}S{center_dot}(B{sub 2}) channel may proceed on adiabatic reaction paths resulting from the coupling of the initially excited state to other low-lying electronic states encountered along the reaction coordinate. Detailed high level ab initio calculations adopting multireference wave functions reveal that the C{sub 6}H{sub 5}S{center_dot}(B{sub 1}) channel may be directly accessed via a {sup 1}(n{sub {pi}},{sigma}*) photoexcitation at 243 nm while the key feature of the photodissociation dynamics of the C{sub 6}H{sub 5}S{center_dot}(B{sub 2}) channel is the involvement of the {sup 3}(n{sub {pi}},{pi}*){yields}{sup 3}(n{sub {sigma}},{sigma}*) profile as well as the spin-orbit induced avoided crossing between the ground and the {sup 3}(n{sub {pi}},{sigma}*) state. The S-D bond dissociation energy of thiophenol-d{sub 1} is accurately estimated to be D{sub 0}=79.6{+-}0.3 kcal/mol. The S-H bond dissociation energy is also estimated to give D{sub 0}=76.8{+-}0.3 kcal/mol, which is smaller than previously reported ones by at least 2 kcal/mol. The C-H bond of the benzene moiety is found to give rise to the H fragment. Ring opening reactions induced by the {pi}-{pi}*/n{sub {pi}}-{pi}* transitions followed by internal conversion may be responsible for the isotropic broad translational energy distribution of fragments.« less

Authors:
; ; ;  [1]
  1. Department of Chemistry and School of Molecular Science (BK21), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701 (Korea, Republic of)
Publication Date:
OSTI Identifier:
20868215
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 3; Other Information: DOI: 10.1063/1.2424939; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANISOTROPY; CHEMICAL BONDS; DEUTERIUM; DIPOLE MOMENTS; DISSOCIATION; DISSOCIATION ENERGY; ENERGY SPECTRA; EXCITED STATES; GROUND STATES; HYDROGEN; MOLECULAR ORBITAL METHOD; PHOTOCHEMISTRY; PHOTOLYSIS; PHOTON-MOLECULE COLLISIONS; RADICALS; REACTION KINETICS; THIOPHENOLS; WAVE FUNCTIONS

Citation Formats

Lim, Ivan S., Lim, Jeong Sik, Lee, Yoon Sup, and Kim, Sang Kyu. Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: Intramolecular orbital alignment of the phenylthiyl radical. United States: N. p., 2007. Web. doi:10.1063/1.2424939.
Lim, Ivan S., Lim, Jeong Sik, Lee, Yoon Sup, & Kim, Sang Kyu. Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: Intramolecular orbital alignment of the phenylthiyl radical. United States. doi:10.1063/1.2424939.
Lim, Ivan S., Lim, Jeong Sik, Lee, Yoon Sup, and Kim, Sang Kyu. Sun . "Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: Intramolecular orbital alignment of the phenylthiyl radical". United States. doi:10.1063/1.2424939.
@article{osti_20868215,
title = {Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: Intramolecular orbital alignment of the phenylthiyl radical},
author = {Lim, Ivan S. and Lim, Jeong Sik and Lee, Yoon Sup and Kim, Sang Kyu},
abstractNote = {The photoinduced hydrogen (or deuterium) detachment reaction of thiophenol (C{sub 6}H{sub 5}SH) or thiophenol-d{sub 1} (C{sub 6}H{sub 5}SD) pumped at 243 nm has been investigated using the H (D) ion velocity map imaging technique. Photodissociation products, corresponding to the two distinct and anisotropic rings observed in the H (or D) ion images, are identified as the two lowest electronic states of phenylthiyl radical (C{sub 6}H{sub 5}S{center_dot}). Ab initio calculations show that the singly occupied molecular orbital of the phenylthiyl radical is localized on the sulfur atom and it is oriented either perpendicular or parallel to the molecular plane for the ground (B{sub 1}) and the first excited state (B{sub 2}) species, respectively. The experimental energy separation between these two states is 2600{+-}200 cm{sup -1} in excellent agreement with the authors' theoretical prediction of 2674 cm{sup -1} at the CASPT2 level. The experimental anisotropy parameter ({beta}) of -1.0{+-}0.05 at the large translational energy of D from the C{sub 6}H{sub 5}SD dissociation indicates that the transition dipole moment associated with this optical transition at 243 nm is perpendicular to the dissociating S-D bond, which in turn suggests an ultrafast D+C{sub 6}H{sub 5}S{center_dot}(B{sub 1}) dissociation channel on a repulsive potential energy surface. The reduced anisotropy parameter of -0.76{+-}0.04 observed at the smaller translational energy of D suggests that the D+C{sub 6}H{sub 5}S{center_dot}(B{sub 2}) channel may proceed on adiabatic reaction paths resulting from the coupling of the initially excited state to other low-lying electronic states encountered along the reaction coordinate. Detailed high level ab initio calculations adopting multireference wave functions reveal that the C{sub 6}H{sub 5}S{center_dot}(B{sub 1}) channel may be directly accessed via a {sup 1}(n{sub {pi}},{sigma}*) photoexcitation at 243 nm while the key feature of the photodissociation dynamics of the C{sub 6}H{sub 5}S{center_dot}(B{sub 2}) channel is the involvement of the {sup 3}(n{sub {pi}},{pi}*){yields}{sup 3}(n{sub {sigma}},{sigma}*) profile as well as the spin-orbit induced avoided crossing between the ground and the {sup 3}(n{sub {pi}},{sigma}*) state. The S-D bond dissociation energy of thiophenol-d{sub 1} is accurately estimated to be D{sub 0}=79.6{+-}0.3 kcal/mol. The S-H bond dissociation energy is also estimated to give D{sub 0}=76.8{+-}0.3 kcal/mol, which is smaller than previously reported ones by at least 2 kcal/mol. The C-H bond of the benzene moiety is found to give rise to the H fragment. Ring opening reactions induced by the {pi}-{pi}*/n{sub {pi}}-{pi}* transitions followed by internal conversion may be responsible for the isotropic broad translational energy distribution of fragments.},
doi = {10.1063/1.2424939},
journal = {Journal of Chemical Physics},
number = 3,
volume = 126,
place = {United States},
year = {Sun Jan 21 00:00:00 EST 2007},
month = {Sun Jan 21 00:00:00 EST 2007}
}