Translational energy distributions of the products of the 193 and 157 nm photodissociation of chloroethylenes

Abstract

The 193 and 157 nm photodissociations of three isomers of dichloroethylene (DCE) and trichloroethylene (TCE) were investigated using a technique of photofragmentation translational spectroscopy. The photofragmentation mechanisms were constructed by analyzing the time-of-flight spectra of C2H2+, Cl+, HCl+, C2HCl+, and C2Cl2+ produced by electron impact of neutral photofragments. In the 193 nm photodissociation, both the HCl elimination and the C–Cl bond rupture were important for all the compounds examined. It was concluded that secondary dissociation of the vibrationally excited chlorinated vinyl radical produced by the C–Cl bond rupture was important even at 193 nm. In the 157 nm photodissociation, the mechanisms were similar to those at 193 nm for cis-DCE, 1,1-DCE, and TCE, while only the C–Cl bond rupture occurred for trans-DCE. This result suggests that the 157 nm photodissociation of trans-DCE proceeds via the direct photodissociation following the photoexcitation to the repulsive nσ*1 state. A minor C–H bond rupture was also found in the 157 nm photodissociations of cis-DCE and TCE. On the basis of the present mechanisms, the translational energy distributions and the branching ratios were estimated for all the possible processes.

The C–Cl bond fissions from the photolysis of CHCl=CCl2 at 193 nm

“…Supported by the experimental observation of the C 2 HCl 2 ϩ signal, we thus obtain two separate P(E t ) distributions for the C-Cl bond fissions as opposed to a single P(E t ) distributions shown in the previous work. 1 For the HCl elimination of reaction ͑1͒, on the other hand, our P(E t ) distribution is in good agreement with their work. 1 Also shown in Table I is the relative product yield for reactions ͑1͒-͑3͒.…”

“…This is precisely the treatment used by Sato et al 1 However, we performed the simulation with a different P(E t ) distribution to represent the dissociating C 2 HCl 2 fragment. The resultant P(E t ) distributions are depicted by the dash-dot-dot and the dot curves in Fig.…”

Probing the Ignored Elimination Channel of Br2 in the 248 nm Photodissociation of 1,1‐Dibromoethylene by Cavity Ring‐Down Absorption Spectroscopy

“…Sato et al observed HCl, Cl, C 2 H 2 , C 2 HCl, and C 2 Cl 2 fragments in the photodissociation of dichloroethylenes and trichloroethylene at 193 and 157 nm. [18] He et al characterized the dissociation channels of H, HCl, ClA C H T U N G T R E N N U N G ( 2 P 3/2 ), and Cl*A C H T U N G T R E N N U N G ( 2 P 1/2 ) in the fragmentation of 1,1-and 1,2-C 2 H 2 Cl 2 at 193 nm. [19] Chandra et al determined the quantum yields of Cl* in the near-UV photodissociation of dichloroethylenes.…”

Photodissociation of 1,2‐Dibromoethylene at 248 nm: Br2 Molecular Elimination Probed by Cavity Ring‐Down Absorption Spectroscopy

“…The photochemistry of ethylene [1][2][3][4][5][6][7][8] and its halogen-substituted derivatives [9][10][11][12][13] has attracted wide interest of both experimentalists and theorists for decades. Upon UV irradiation, ethylene is excited to the (p, p*) state, which may result in dissociation to yield H + C 2 H 3 , 2H+ HCCH, and H 2 + HCCH fragments through three-and four-center elimination and H-migration reactions.…”

“…[16] Resende and DeAlmeida reduced the activation energy to 407 kJ mol À1 by involving an intermediate of Cl and a C 2 H 2 Cl radical in the calculation. [17] From an experimental point of view, when the dichloroethylene species were irradiated at 193 nm, [9] no Cl 2 fragments were detected, probably because the high energy barrier makes the dissociation process difficult. Even at a shorter wavelength (namely, 157 nm), the photodissociation of F 2 CCH 2 and F 2 CCFH gave rise to HF, H 2, H, and F elimination, as well as to double-bond breaking, but not to the release of F 2 .…”