Guang-Jun Wang

Photodissociation of bromobenzene at 266 nm

The photodissociation of C6H5Br at 266 nm has been investigated on the universal crossed molecular beam machine, and time-of-flight spectra as well as the angular distribution of Br atom have been measured. Photofragment translational energy distribution P(Et) reveals that about 47% of the available energy is partitioned into translational energy. The anisotropy parameter β at this wavelength is −0.7±0.2. From P(Et) and β, we deduce that C6H5Br photodissociation is a fast process and the transition dipole moment is almost perpendicular to the C–Br bond. Ab initio calculations have been performed, and the calculated results show that the geometry of the first excited state of bromobenzene has changed apparently compared with that of the ground state. Two kinds of possible fast dissociation mechanism have also been proposed.

Photodissociation of chlorobenzene at 266 nm

Abstract The photodissociation of C 6 H 5 Cl at 266 nm has been investigated using the crossed laser–molecular beam technique. The translational energy distribution of the Cl photofragment is obtained. The TOF spectrum of the Cl fragment consists of only one component. Ab initio calculation shows that the first excited state of chlorobenzene has large geometry changes compared to that of the ground state. The hot molecule mechanism is considered to be probable for the dissociation of C 6 H 5 Cl at 266 nm.

Photodissociation of o-dichlorobenzene at 266 nm

Abstract The photodissociation o -dichlorobenzene at 266 nm has been investigated using the universal crossed molecular beam technique. Photofragment translational energy distribution P ( E t ) and angular distribution of photofragments have been obtained and it is estimated that 23% of the available energy is assigned to translational energy. The anisotropy parameter is determined to be 0.4. From P ( E t ) and β we deduce that o -C 6 H 4 Cl 2 photodissociation is a slow process. Ab initio calculation has been performed and it shows that the parent molecule has a larger geometry deformation in its excited states comparing with that of the ground state. The possible dissociation mechanism has also been proposed.

Photodissociation of m-bromotoluene at 266 nm

Abstract The photodissociation of m-bromotoluene at 266 nm has been investigated on the universal crossed molecular beam machine, and the time-of-flight (TOF) spectra of recoiling photofragment at different angles were measured with the photofragment translational spectroscopy (PTS) detecting technique. The observed TOF spectra indicate that there are two different dissociation channels, one is channel (A) β=0.7±0.1 and 〈Et〉=3.76±0.5 kcal/mol, the other is channel (B) β=0.2±0.15 and 〈Et〉=12.13±0.5 kcal/mol. To better interpret the experimental results and primary photodissociation mechanism, the ultraviolet–visible (UV) absorption spectra of m-, o- and p-bromotoluene were measured, and the geometries of m-bromotoluene were optimized at the CASSCF(8,7)/6-311G** level. Two probable photodissociation mechanisms are suggested based upon the experimental results and the ab initio calculation.

Substitution effects of methyl: photodissociation of m-, o- and p-chlorotoluene at 266 nm

The photodissociation dynamics of m-, o- and p-chlorotoluene at 266 nm was studied using the universal crossed molecular beams machine and photofragment translational spectroscopy (PTS) technique. The time-of-flight (TOF) spectra of Cl and C7H7 photofragments were measured at different angles. By employing both forward convolution method and least-squares fitting method, the TOF spectra of photofragments (Cl and C7H7) and the angular distribution of Cl are fitted, at the same time the translational energy distributions of photofragment and anisotropy parameters (β) have been derived. The geometries of the ground state, the first excited state and the triplet state have been optimized using CASSCF(8,7)/6-311G** method. The transition electronic dipole moments were calculated at the CIS/6-311G* level. The calculation results are in good agreement with the experiment. Plausible photodissociation mechanisms are proposed and the substitution effects of methyl are discussed.

Photofragment translational spectroscopy of p-bromotoluene at 266 nm

Abstract Photodissociation of p -bromotoluene at 266 nm has been investigated on the universal crossed molecular beam machine, and translational energy distribution P ( E t ) as well as the anisotropy parameter β have been obtained. Photofragment translational energy distribution P ( E t ) reveals that ∼38.5% of the available energy is partitioned into translational energy. The anisotropy parameter β is determined to be −0.4±0.2. From P ( E t ) and β , we deduce that p -bromotoluene photodissociation is a fast process and the perpendicular transition plays a central role at this wavelength. The possible mechanism has been discussed and comparison of p -bromotoluene with bromobenzene, o -bromotoluene has also been made.

Photodissociation of o-bromotoluene at 266 nm

Abstract The photodissociation of o -bromotoluene at 266 nm has been investigated using the universal crossed laser–molecular beam technique. The angle-resolved time-of-flight (TOF) spectra corresponding to Br photofragment are measured at different lab angles. The observed translational energy distribution and anisotropy parameters of the Br photofragment indicate that o -bromotoluene dissociates via two channels. In the first channel, the anisotropy parameter β is determined to be 0.5±0.2 and the average translational energy is only 9% of the available energy. In the other photofragmentation channel, β is determined to be −0.4±0.2 and 44% of the available energy is assigned to translational energy. Possible mechanisms are discussed.

Photodissociation of 1-bromo-2-chloroethane at 266 nm

The photodissociation of CH2BrCH2Cl at 266 nm has been investigated on the universal crossed molecular beam machine. The primary dissociation step leads exclusively to the formation of CH2CH2Cl radicals and Br atoms in the electronic ground state as well as in the spin-orbit excited state, with a branching ratio 2 +/- 1:8 +/- 1. Photofragment total c.m. translational energy distribution P(E-t) has been obtained and about 64% of the available energy is partitioned into translational energy for Br channel and about 28.5% of the available energy is partitioned into translational energy for Br* channel. The anisotropy parameters are determined to be beta(Br*) = 0.8 +/- 0.2 and beta(Br) = -0.6 +/- 0.2, respectively. Some CH2CH2Cl radicals with large internal excitation (corresponding to formation of ground state Br channel) may undergo secondary dissociation to form CH2CH2 +/- Cl. The experimental results are discussed in terms of a model that involves the initial excitation of two repulsive electronic states: one from an parallel transition to the (3)Q(0) state, and the other from a perpendicular transition to the (3)Q(1), (1)Q states

Reactive scattering of crossed supersonic beams: Cl+ CH I I Cl+ CH I 2 2 2

The reaction Cl + CH2I→ICl + CH2I has been studied at a relative collision energy of 53·2kJ mol-1 using the crossed-beam technique. Angular and translational energy distributions of reactive scattered ICl products have been measured. The angular distribution is consistent with reaction occurring through a short-lived complex with lifetime about 0·8 of the rotational period. The kinetic energy distributions measured for this system show strong coupling to scattering angles. The forward- and backward-scattered products have higher translational energy than those that are sideways scattered. A phase-space model is developed which explains the experimental energy distributions well.