A concerted three-body formation X+Y+C2H4 in the photodissociation of CH2XCH2Y (X,Y=Br,Cl) at 193 nm

BrCl+ elimination from Coulomb explosion of 1,2-bromochloroethane induced by intense femtosecond laser fields

By using a dc-slice imaging technique, photodissociation of 1,2-C₂H₄BrCl was investigated at 800 nm looking for heteronuclear unimolecular ion elimination of BrCl⁺ in an 80 fs laser field. The occurrence of fragment ion BrCl⁺ in the mass spectrum verified the existence of a unimolecular decomposition channel of BrCl⁺ in this experiment. The relative quantum yield of the BrCl⁺ channel was measured to be 0.8%. By processing and analyzing the velocity and angular distributions obtained from the corresponding sliced images of BrCl⁺ and its partner ion C₂H₄⁺, we concluded that BrCl⁺ came from Coulomb explosion of the 1,2-bromochloroethane dication 1,2-C₂H₄BrCl²⁺. With the aid of quantum chemical calculations at the M06-2X/def2-TZVP level, the potential energy surface for BrCl⁺ detachment from 1,2-C₂H₄BrCl²⁺ has been examined in detail. According to the ab initio calculations, two transition state structures tended to correlate with the reactant 1,2-C₂H₄BrCl²⁺ and the products BrCl⁺ + C₂H₄⁺. In this entire dissociation process, the C–Br and C–Cl bond lengths were observed to elongate asymmetrically, that is, the C–Br chemical bond broke firstly, and subsequently a new Br–Cl chemical bond started to emerge while the C–Cl bond continued to exist for a while. Hence, an asynchronous concerted elimination mechanism was favored for BrCl⁺ detachment.

Concerted elimination of the molecular ion BrCl⁺ from Coulomb explosion of 1,2-bromochloroethane was studied theoretically and experimentally.

Investigation of 3-fragment photodissociation of O3 at 193.4 and 157.6 nm by coincident measurements

Photodissociation of the ozone molecule at 193.4 nm (6.41 eV) and 157.6 nm (7.87 eV) is studied by fast-beam translational spectroscopy. Coincident detection of the dissociation products allows direct observation of the 3-fragment channel and determination of its kinematic parameters. The results indicate that at each wavelength, 3-fragment dissociation proceeds through synchronous concerted bond breaking, but the energy partitioning among the fragments is different. The branching fraction of the 3-fragment channel increases from 5.2(6)% at 193.4 nm to 26(4)% at 157.6 nm, in agreement with previous studies. It is shown that vibrational excitation of the symmetric stretch mode in O3 molecules created by photodetachment of O(3)(-) anion enhances the absorption efficiency, especially at 193.4 nm, but does not have a strong effect on the 3-fragment dissociation.

Coulomb explosion and dissociative ionization of 1,2-dibromoethane under an intense femtosecond laser field

Coulomb explosion and dissociative ionization of 1,2-dibromoethane are experimentally investigated in a near-infrared (800 nm) femtosecond laser field by dc-slice imaging technology.