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Gas‐Phase Photodissociation of CH 3 CHBrCOCl at 248 nm: Detection of Molecular Fragments by Time‐Resolved FT‐IR Spectroscopy
Author(s) -
Liu ChiaYun,
Tsai MingTsang,
Tsai PoYu,
Liu YuTing,
Chen Si Ying,
Chang Agnes Hsiu Hwa,
Lin KingChuen
Publication year - 2011
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201000713
Subject(s) - photodissociation , spectroscopy , gas phase , phase (matter) , chemistry , molecular spectroscopy , analytical chemistry (journal) , infrared spectroscopy , photochemistry , materials science , physics , organic chemistry , quantum mechanics
By employing time‐resolved Fourier transform infrared emission spectroscopy, the fragments HCl ( v =1–3), HBr ( v =1), and CO ( v =1‐3) are detected in one‐photon dissociation of 2‐bromopropionyl chloride (CH 3 CHBrCOCl) at 248 nm. Ar gas is added to induce internal conversion and to enhance the fragment yields. The time‐resolved high‐resolution spectra of HCl and CO were analyzed to determine the rovibrational energy deposition of 10.0±0.2 and 7.4±0.6 kcal mol −1 , respectively, while the rotational energy in HBr is evaluated to be 0.9±0.1 kcal mol −1 . The branching ratio of HCl( v >0)/HBr( v >0) is estimated to be 1:0.53. The bond selectivity of halide formation in the photolysis follows the same trend as the halogen atom elimination. The probability of HCl contribution from a hot Cl reaction with the precursor is negligible according to the measurements of HCl amount by adding an active reagent, Br 2 , in the system. The HCl elimination channel under Ar addition is verified to be slower by two orders of magnitude than the Cl elimination channel. With the aid of ab initio calculations, the observed fragments are dissociated from the hot ground state CH 3 CHBrCOCl. A two‐body dissociation channel is favored leading to either HCl+CH 3 CBrCO or HBr+CH 2 CHCOCl, in which the CH 3 CBrCO moiety may further undergo secondary dissociation to release CO.