Photofragment imaging: the 205-nm photodissociation of CH3Br and CD3Br

Product vibrational distributions in CH3Br photodissociation

“…Even if some rotational excitation of the fragments has been observed [12,13], it corresponds to a small amount of energy (<0.1 eV) as compared to the one related to translation (%3 eV) or vibration (%0.3 eV). All experiments performed on CH 3 Br converge on the fact that methyl product is vibrationally hotter, especially in the umbrella mode m 2 , when it is formed in conjunction with ground spin-orbit state Br rather than with the excited one Br * [9][10][11][12][13][14]. A similar trend was systematically observed on other methyl-halides like CH 3 I [19], although less pronounced than in methyl-bromide [20,21,6].…”

“…However, methyl iodine is the most extensively studied methyl halide system with respect to UV photodissociation (references are given in [3][4][5][6]). By contrast, there is a limited number of experimental studies [7][8][9][10][11][12][13][14] on CH 3 Br and quantitative studies involving ab initio potential energy surfaces (PES) have been undertaken only recently [15][16][17]. These theoretical studies involved however a single degree of freedom, the methyl-bromine distance.…”

“…One aim of the present Letter is to extend these recent studies by providing information on product state vibrational distributions using ab initio calculations involving two degrees of freedom, the methyl-bromine distance and the methyl umbrella angle, in conjunction with wave packet dynamical simulations. The selection of only two degrees of freedom, the methyl-bromine stretch m 3 and the methyl umbrella m 2 modes, is justified by the fact that it is known from experiments [9][10][11][12][13][14] that most of the available energy goes into recoil methyl-bromine translational energy (related to m 3 ) and into methyl umbrella excitation (m 2 ). Even if some rotational excitation of the fragments has been observed [12,13], it corresponds to a small amount of energy (<0.1 eV) as compared to the one related to translation (%3 eV) or vibration (%0.3 eV).…”

Photodissociation Dynamics

“…96 One can also perform somewhat less detailed experiments in which atomic photofragments are state-specifically ionized and analyzed via photofragment imaging. [97][98][99][100][101] The results of ref 100 are of particular interest as they provided the first evidence for the production of highly vibrationally excited O 2 ( 3 Σ g -) from O 3 photolysis; this product may be partially responsible for stratospheric O 3 production.…”

Perspective: Advanced particle imaging

“…Many of these were reviewed in 1995. 21 The first applications were to further study the dissociation of methyl iodide and its deuterated derivative [22][23][24][25] as well as H 2 S, 22 but further work was performed on methyl bromide, 26 methane, 27 acetylene, 28 and van der Waals molecules. 29 At the same time, product imaging was used for the first time to study bimolecular reactions, for example, H + HI 30 and H + D 2 , 31 and to analyze crossed-beam studies of an energy transfer process, Ar + NO(v = 0, J = 0) → Ar + NO(v = 0, J).…”