Primary and Secondary Processes in the Photodissociation of CHBr₃

Abstract

The photodissociation of CHBr3 at 193 run has been investigated using photo fragment translational spectroscopy with VUV ionization detection. The only primary process observed was the loss of bromine atom. The translational energy distribution for this channel suggests a direct dissociation from an excited electronic state, and the anisotropy parameter, fJ=O.O, is consistent with a transition dipole moment aligned perpendicular to C 3 v axis. The majority of nascent CHBr2 fragments undergo secondary dissociation via two competing channels. The elimination ofHBr and C-Br bond cleavage in CHBr 2 occur with comparable yields. We also provide ab initio calculations on the relevant photochemical species and RRKM estimates of the product branching ratios that are consistent with the experimental observations.

Haloform adsorption on crystalline copolymer films of vinylidene fluoride with trifluoroethylene

“…Indeed, the main bromine 3d core photoemission intensity increases with coverage, but after each annealing treatment to room temperature, the bromine signal is lost, indicative of bromoform desorption (Figure 3a). Following adsorption on P(VDF-TrFE) at 120 K and photofragmentation of the adsorbed bromoform on P(VDF-TrFE) (as in [9,10,43]), the bromine 3d core level signal is persistent to room temperature and above (120 °C) ( Figure 5). We must infer that dissociative adsorption is not readily reversible and bromine signals, characteristic of molecular fragments, are persistent in XPS to well above room temperature on P(VDF-TrFE) (although not so on graphite), so we attribute the spectra in Figure 2 to molecular on P(VDF-TrFE), not dissociative adsorption.…”

Theoretical investigation of the structures and properties of fluoromethyl peroxyl radicals

“…The overall reactivity of haloalkyl radicals has been found to be strongly correlated to the COH bond dissociation energies (BDEs) of the parent haloalkanes [43]. Because the reactivity of the peroxyl radicals is strongly dependent on the stability of their alkyl radicals, we will discuss such stability in terms of the COH BDEs of the parent fluoromethanes.…”

“…Because the reactivity of the peroxyl radicals is strongly dependent on the stability of their alkyl radicals, we will discuss such stability in terms of the COH BDEs of the parent fluoromethanes. Although the COH BDEs of halomethanes have been previously estimated at high ab initio levels of theory [43], the present estimation will enable us to judge the DFT performance with respect to high ab initio methods in predicting the BDEs and the substituent effects trends.…”

“…COH BDEs calculated at different levels of theory for methane and fluoromethanes [24,[43][44][45] are given in Table VI ) are calculated at the HF and B3LYP levels of theory using 6-31G(d,p) basis set with 0.8929 and 0.9806 scaling of the vibrational frequencies, respectively.…”

Reaction of CH3O2 and HO2: Ab initio characterization of dimer structure and vibrational mode analysis for reaction mechanisms

“…Their channels must be searched to control the forms of products. Recently, analysis of the vibrational mode and the vibrational frequencies for the intermediates and the transition states have attracted the attention of Mann and Hase [6] and McGivern et al [7] for the S N 2 reaction Cl Ϫ ϩ CH 3 Cl and the calculation of the dissociation energy of COH and COX, respectively. In this article, we investigate the channel of CH 3 O 2 ϩ HO 2 reaction.…”