Photodissociation of Benzoyl Chloride: A Velocity Map Imaging Study Using VUV Detection of Chlorine Atoms

Abstract

UV photodissociation of benzoyl chloride, Ph−CO−Cl, is associated with the loss of a chlorine atom. Here we excite benzoyl chloride to the S 1 , S 2 , and S 3 excited states at 237, 253, 265, and 279.6 nm and detect the Cl photofragment by [1 + 1′] photoionization using 118.9 nm VUV radiation. The translational energy distribution of the Cl atom is measured by velocity map ion imaging. An isotropic image and a unimodal translational energy distribution are observed at all dissociation wavelengths, and a fraction of 18−20% of the excess energy is released into translation. The results indicate a dissociation that predominately proceeds from the vibrationally hot S 0 ground state, although the observed translational energy release deviates significantly from a prior distribution. However, the impulsive model does also not represent the translational energy release. As a Cl/Cl* branching ratio of 9:1 or more is observed in one-color experiments at 235 nm, we conclude that direct dissociation from excited electronic states contributes only to a minor extent.

Dynamics of methyl radical formation by 266 nm photolysis of xylenes and mesitylene

“…It is known that a=1 in equation ( 2) indicates non-statistical TKER distribution. 39 Moreover, deviations on the higher kinetic energy side, originating due to multiphoton detection of the methyl radical, which appear to be only marginal in the present case, have been neglected. 39 Interestingly, the value of 'b' (from equation 2) are very similar for all the three isomers of xylene (4.87, 4.61 and 4.32 for ortho, meta and para isomers, respectively) and moderately different from mesitylene (5.20), which suggests that overall dynamics of methyl radical formation is insensitive to the position of substitution in xylenes but marginally dependent on the number of methyl groups.…”

“…Further, the TKER distribution profiles of the methyl fragments were fitted to an empirical function given by equation (2). [37][38][39] 𝑃(𝐸 𝑇 ) = 𝐶 • (𝐸 𝑇 ) 𝑎 • (𝐸 𝑇 𝑚𝑎𝑥 − 𝐸 𝑇 ) 𝑏…”

Photodissociation of the trichloromethyl radical: photofragment imaging and femtosecond photoelectron spectroscopy

“…The ns-experiments were conducted at the University of Würzburg, using a photofragment imaging setup. 42,45 A skimmed free molecular jet enters the time of flight mass spectrometer (TOF-MS), which can be operated in either space-focusing or VMI configuration. Two separate counterpropagating ns-laser systems were used to dissociate and ionize the fragments.…”

“…Note that the spin-orbit excited 2 P1/2 state of Cl cannot be probed by this scheme, as discussed previously, because there is no suitable transition in the tripling range accessible with the setup. 45 For these experiments, the dye laser was scanned over the entire Doppler profile of the atomic transition. The residual 356.7 nm light was employed for the ionisation step.…”

“…In the past, we applied the method to investigate H-atom loss from radicals, 42 biradicals 43 and carbenes, 44 but recently extended our work to chlorine-containing molecules. 45 Experiments are accompanied by computations using time-dependent density functional theory (TD-DFT).…”