Determining the CH{sub 3}SO{sub 2}{yields}CH{sub 3}+SO{sub 2} barrier from methylsulfonyl chloride photodissociation at 193 nm using velocity map imaging

Journal Article · Tue Jul 28 04:00:00 EDT 2009 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3159556· OSTI ID:21559746

Ratliff, Britni J; Xiaonan, Tang; Butler, Laurie J ^[1]; Szpunar, David E ^[2]; Lau, Kai-Chung ^[3]

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1. Department of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States)
2. Department of Biological, Chemical, and Physical Sciences, Roosevelt University, Schaumburg, Illinois 60173 (United States)
3. Department of Biology and Chemistry, City University of Hong Kong (Hong Kong)

These imaging experiments study the formation of the methylsulfonyl radical, CH{sub 3}SO{sub 2}, from the photodissociation of CH{sub 3}SO{sub 2}Cl at 193 nm and determine the energetic barrier for the radical's subsequent dissociation to CH{sub 3}+SO{sub 2}. We first state-selectively detect the angular and recoil velocity distributions of the Cl({sup 2}P{sub 3/2}) and Cl({sup 2}P{sub 1/2}) atoms to further refine the distribution of internal energy partitioned to the momentum-matched CH{sub 3}SO{sub 2} radicals. The internal energy distribution of the radicals is bimodal, indicating that CH{sub 3}SO{sub 2} is formed in both the ground state and low-lying excited electronic states. All electronically excited CH{sub 3}SO{sub 2} radicals dissociate, while those formed in the ground electronic state have an internal energy distribution which spans the dissociation barrier to CH{sub 3}+SO{sub 2}. We detect the recoil velocities of the energetically stable methylsulfonyl radicals with 118 nm photoionization. Comparison of the total recoil translational energy distribution for all radicals to the distribution obtained from the detection of stable radicals yields an onset for dissociation at a translational energy of 70{+-}2 kcal/mol. This onset allows us to derive a CH{sub 3}SO{sub 2}{yields}CH{sub 3}+SO{sub 2} barrier height of 14{+-}2 kcal/mol; this determination relies on the S-Cl bond dissociation energy, taken here as the CCSD(T) predicted energy of 65.6 kcal/mol. With 118 nm photoionization, we also detect the velocity distribution of the CH{sub 3} radicals produced in this experiment. Using the velocity distributions of the SO{sub 2} products from the dissociation of CH{sub 3}SO{sub 2} to CH{sub 3}+SO{sub 2} presented in the following paper, we show that our fastest detected methyl radicals are not from these radical dissociation channels, but rather from a primary S-CH{sub 3} bond photofission channel in CH{sub 3}SO{sub 2}Cl. We also present critical points on the ground state potential energy surface of CH{sub 3}SO{sub 2} at the //CCSD(T)/aug-cc-pV(Q+d)ZCCSD(T)/6-311++G(2df,p) level. We include harmonic zero-point vibrational corrections as well as core-valence and scalar-relativistic corrections. The CCSD(T) predicted barrier of 14.6 kcal/mol for CH{sub 3}SO{sub 2}{yields}CH{sub 3}+SO{sub 2} agrees well with our experimental measurement. These results allow us to predict the unimolecular dissociation kinetics of CH{sub 3}SO{sub 2} radicals and critique the analysis of prior time-resolved photoionization studies on this system.

• OSTI ID: 21559746
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 4 Vol. 131; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ALKYL RADICALS
CHALCOGENIDES
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
COMPARATIVE EVALUATIONS
DECOMPOSITION
DETECTION
DISSOCIATION
DISSOCIATION ENERGY
DISTRIBUTION
ENERGY
ENERGY LEVELS
ENERGY RANGE
ENERGY SPECTRA
EVALUATION
EXCITED STATES
FISSION
GROUND STATES
HALIDES
HALOGEN COMPOUNDS
IONIZATION
METHYL RADICALS
NUCLEAR REACTIONS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOFISSION
PHOTOIONIZATION
PHOTOLYSIS
PHOTONUCLEAR REACTIONS
POTENTIAL ENERGY
RADICALS
RECOILS
RELATIVISTIC RANGE
SPECTRA
SULFUR COMPOUNDS
SULFUR DIOXIDE
SULFUR OXIDES
VELOCITY
VIBRATIONAL STATES