Photochemistry of CH 3 Cl: Dissociation and CH···Cl Hydrogen Bond Formation
Abstract
State-of-the-art electronic structure calculations (MR-CISD) are used to map five different dissociation channels of CH 3 Cl along the C-Cl coordinate: i) CH 3 (X 2 A 2´´) + Cl(2 P), ii) CH 3 (3s 2 A 1´) + Cl(2 P), iii) CH 3 + (1 A 1´) + Cl (1 S), iv) CH 3 (3p 2 E´) + Cl(2 P), and v) CH 3 (3p 2 A 2´´) + Cl(2 P). By the first time these latter four dissociation channels, accessible upon VUV absorption, are described. The corresponding dissociation limits, obtained at the MR-CISD+Q level, are 3.70, 9.50, 10.08, 10.76, and 11.01 eV. The first channel can be accessed through n* and n3s states, while the second channel can be accessed through n e 3s, n e 3p , and 3s states. The third channel, corresponding to the CH 3 + + Cl ion-pair, is accessed through n e 3p e states. The fourth is accessed through n e 3p e , n e 3p , and 3p , while the fifth through 3p e and CH * states. The population of the diverse channels is controlled by two geometrical spots, where intersections between multiple states allow a cascade of nonadiabatic events. The ion-pair dissociation occurs through formation of CH 3 + •••Cl and H 2 CH + •••Cl intermediate complexes bound by 3.69 and 4.65 eV. The enhanced stability of the H 2 CH + •••Cl complex is due to a CH•••Cl hydrogen bond. A time-resolved spectroscopic setup is proposed to detect those complexes.
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