Ground and Excited State Dissociation Dynamics of Ionized 1,1-Difluoroethene

Abstract

The kinetic energy release distributions (KERDs) for the fluorine atom loss from the 1,1-difluoroethene cation have been recorded with two spectrometers in two different energy ranges. A first experiment uses dissociative photoionization with the He(I) and Ne(I) resonance lines, providing the ions with a broad internal energy range, up to 7 eV above the dissociation threshold. The second experiment samples the metastable range, and the average ion internal energy is limited to about 0.2 eV above the threshold. In both energy domains, KERDs are found to be bimodal. Each component has been analyzed by the maximum entropy method. The narrow, low kinetic energy components display for both experiments the characteristics of a statistical, simple bond cleavage reaction: constraint equal to the square root of the fragment kinetic energy and ergodicity index higher than 90%. Furthermore, this component is satisfactorily accounted for in the metastable time scale by the orbiting transition state theory. Potential energy surfaces corresponding to the five lowest electronic states of the dissociating 1,1-C2H2F2+ ion have been investigated by ab initio calculations at various levels. The equilibrium geometry of these states, their dissociation energies, and their vibrational wavenumbers have been calculated, and a few conical intersections between these surfaces have been identified. It comes out that the ionic ground state X2B1 is adiabatically correlated with the lowest dissociation asymptote. Its potential energy curve increases in a monotonic way along the reaction coordinate, giving rise to the narrow KERD component. Two states embedded in the third photoelectron band (B2A1 at 15.95 eV and C2B2 at 16.17 eV) also correlate with the lowest asymptote at 14.24 eV. We suggest that their repulsive behavior along the reaction coordinate be responsible for the KERD high kinetic energy contribution.

Vibrational and electronic excitations in fluorinated ethene cations from the ground up

“…This multiple channel F-loss mechanism explains the proposed bimodal kinetic energy release distribution observed for C 2 H 3 F + and 1,1-C 2 F 2 H 2 + , 12,13,42 as the low kinetic energy release modus is a result of the statistical dissociation pathway. Furthermore, directC-state involvement is not necessarily required in threshold photoionization.…”

“…[10][11][12][13] Contrary to F-loss from C 2 F 4 + , detailed kinetic energy release studies have shown that F-loss from C 2 H 3 F + and 1,1-C 2 H 2 F 2 + is, in part, an impulsive process. 11,42 The F-loss threshold ion yield curves were shown to correlate only approximately with the TPES signal, 9 which indicates a complex mechanism with possible Rydberg-state involvement. In contrast to C 2 F 4 + , the state which leads unhindered to F-loss is not the first electronically excited state of the parent ion in the other members of the series.…”

The vacuum UV photoabsorption spectroscopy of vinyl fluoride (C2H3F): The vibrational fine structure and its analysis

“…The systematic study of ethylene and of several of its halogen substituted derivatives has been initiated, e.g. for C 2 H 3 Cl [12,13], C 2 H 3 Br [14][15][16] and 1,1-C 2 H 2 F 2 [17,18], or is in progress using the same array of techniques. The vacuum UV spectroscopic data reported on vinyl fluoride are very scarce.…”

Analysis of kinetic energy release distributions by the maximum entropy method

“…In many cases [22,[37][38][39][40][41][42][43][44], the very simple expression (10) is found to provide a very good approximation to P(ε|E) if the value of the exponent k is adequately chosen. A value of k equal to 1/2 or to 1 is usually found.…”

“…A value of k equal to 1/2 or to 1 is usually found. For electronically adiabatic barrierless reactions studied at not too high energies, the appropriate value of k has been observed to be equal to 1/2 [22,[37][38][39][40][41]43,44]. Then, the actual KERD is related to the prior distribution by the following equation:…”