Photoinduced Near Ultraviolet Three Body Decay of Phosgene

Abstract

Faced with the problem of underdetermined kinetic equations in analyzing momenta and kinetic energies of three body decay fragments, we followed two conceptually different paths in order to shed light on the dynamics of the process. One is based on the evaluation of the observed kinematic quantities after introduction of physically meaningful parameters for each type of decay: sequential, synchronously concerted, and asynchronously concerted mechanism. The other one is based on an information theoretic approach, maximizing the entropy of the joint probability matrix containing the probabilities for coincidently realizing accessible sets of product states. The results obtained in both cases match remarkably well: No significant contribution of a molecular channel, producing chlorine molecules, was found. Likewise, the generation of a stable chloroformyl radical had been ruled out in previous studies, so that every dissociation process upon irradiation around 230 nm yields three fragments: two chlorine atoms and a carbon monoxide molecule. For this three body decay, the asynchronously concerted mechanism is the dominant dissociation channel, accounting for over 80% of the products. The chlorine fragments move preferentially in the same direction, resulting in forward scattering of the carbon monoxide. A less abundant decay channel is the synchronously concerted mechanism, in which the two bonds cleave in unison, and that accounts for the remaining products. The geometry of the decaying parent resembles the ground state equilibrium geometry with significant excitations of the COCl 2 bending modes. For both mechanisms the CO fragments are generated with high internal excitation.

Photodissociation of phosgene: Theoretical evidence for the ultrafast and synchronous concerted three-body process

“…Dynamic information of two-body decay can be obtained through straightforward experiments. 3,[10][11][12][13][14][15][16][17][18][19] The mechanistic controversy for a multiplebody decay stems from the challenges of characterizing dissociation at a molecular level. 1,2 There are about 30 systems that were characterized to be capable of three-body photodissociation up to date.…”

“…3,[10][11][12][13][14][15][16][17][18][19] The mechanistic controversy for a multiplebody decay stems from the challenges of characterizing dissociation at a molecular level. [15][16][17] A less abundant decay channel is the synchronously concerted mechanism, in which the two C-Cl bonds cleave in unison. Early studies [10][11][12] led to the proposition of a sequential decomposition mechanism via formation of the thermally instable chloroformyl ͑ClCO͒ radical with immediate subsequent decay into CO and Cl.…”

Fragment Correlation in the Three-Body Breakup of Triatomic Hydrogen

“…This is an open decay channel for all electronically excited states of H 3 . For larger molecules, three-body decay may constitute a major fragmentation pathway and has come into the focus of recent investigations [11][12][13][14]. In the case of H 3 , Peterson et al [15] found evidence for this process in dissociative charge transfer of H 1 3 in Cs, and Datz et al [16] measured the branching between two-body and three-body channels in dissociative recombination of H 1 3 with electrons.…”

Photodissociation dynamics of phosgene: New observations by applying a three-dimensional imaging technique

“…Carbonyl compounds are known to exhibit a complex fragmentation scheme upon irradiation by ultraviolet light because of their small threshold energy with respect to threebody decay. The decay dynamics of acetone, 1 carbonyl cyanides, 2-5 acetyl halides, 6,7 and phosgene [8][9][10] have been investigated by almost any technique offered by modern reaction dynamics, among them nonresonant and resonance enhanced photofragment translational spectroscopy, photofragment imaging, velocity-map imaging and ultrafast spectroscopy. Earlier work is compiled in a review paper about photoinduced three-body decay.…”

“…when irradiated by light at 235 nm in the peak of the first absorption band. 9 The alternative two-body channels produce a͒ Permanent address: Institute of Chemical Kinetics and Combustion, 630090 Novosibirsk, Russia.…”