Photodissociation of cis-, trans-, and 1,1-Dichloroethylene in the Ultraviolet Range: Characterization of Cl(²P_J) Elimination

Abstract

By using photofragment velocity imaging detection coupled with a (2 + 1) resonance-enhanced multiphoton ionization technique, the elimination channel of spin-orbit chlorine atoms in photodissociation of cis-, trans-, and 1,1-dichloroethylene at two photolysis wavelengths of 214.5 and 235 nm is investigated. Translational energy and angular distributions of Cl((2)P(J)) fragmentation are acquired. The Cl((2)P(J)) fragments are produced by two competing channels. The fast dissociation component with higher translational energy is characterized by a Gaussian distribution, resulting from a curve crossing of the initially excited (pi, pi*) state to nearby repulsive (pi, sigma*) and/or (n, sigma*). In contrast, the slow component with a lower translational energy is characterized by a Boltzmann distribution, which dissociates on the vibrationally hot ground state relaxed from the (pi, pi*) state via internal conversion. cis-C(2)H(2)Cl(2) is found to have a larger branching of Boltzmann component than the other two isomers. The fraction of available energy partitioning into translation increases along the trend of cis- < trans- < 1,1-C(2)H(2)Cl(2). This trend may be fitted by a rigid radical model and interpreted by means of a torque generated during the C-Cl bond cleavage. The anisotropy parameters are determined, and the transition dipole moments are expected to be essentially along the C horizontal lineC bond axis. The results are also predicted theoretically. The relative quantum yields of Cl((2)P(J)) have a similar value for the three isomers at the two photolysis wavelengths.

The vacuum UV photoabsorption spectrum of the geminal dichloroethylene (1,1-C2H2Cl2) in the 5–20 eV range. A vibrational analysis of the valence and Rydberg states

“…Our quantum chemical calculations reveal important C-Cl bond lengthening at the optimized geometry of this state which could be nearly repulsive (see table 3). Several photodissociation studies have been reported in the wavelength region of 155-250 nm (8.00-4.96 eV) [7] or 222-304 nm (5.58-4.08 eV) [24] or at 214.5 nm (5.78 eV) and at 235 nm (5.28 eV) [25]. The loss of HCl [7] and Cl( 2 P J ) [24,25] were investigated.…”

Megawatt Ultraviolet Laser Photolysis of Dichloroethenes for Gas-Phase Deposition of Nanosized Chlorinated Soot

“…We thus assume that the earlier observed H and Cl formation and Cl 2 , HCl, and H 2 elimination, ,,, along with the formation and rearrangement of three-membered cyclic compounds, are ensued by further C−H and C−Cl bond homolyses, rearrangements, molecular (Cl 2 , HCl, and H 2 ) elimination, and carbene additions, allowing formation of high-molecular C/H/Cl unsaturates. The observed three- and four-carbon compounds serve as examples of intermediate products arising from addition of carbenes and/or addition/recombination of C-centered radicals, while the observed dichloromethane and trichloromethane illustrate the possibility of cleavage of bonds between carbon atoms in intermediary products.…”

“…These compounds are considered to belong among hazardous materials, and their carbonization to cokes as well as mechanistic studies on their thermal decomposition have attracted only limited attention. The dichloroethenes are well-known to be UV photolyzed via a number of pathways (cleavage of HCl, Cl, and H 2 − ) and to allow formation of C/H/Cl fragments whose recombination in the gas phase may result in deposition of carbon nanoparticles with Cl−C bonds. Such products of UV laser-induced carbonization of chloroethenes have not been yet studied, and we report on ArF and KrF laser photolysis of gaseous cis -, trans -, and gem -dichloroethenes and elucidate the structure of the gas-phase deposited products.…”