Recoil energy distributions for dissociation of the van der Waals molecule p-difluorobenzene–Ar with 450–3000cm−1 excess energy

Abstract

Velocity map imaging has been used to measure the distributions of translational energy released in the dissociation of p-difluorobenzene-Ar van der Waals complexes from the 5 1 , 3 1 , 5 2 , 3 1 5 1 , 5 3 , 3 2 , and 3 2 5 1 states. These states span 818-3317 cm −1 of vibrational energy and correspond to a range of energies above dissociation of 451-2950 cm −1 . The translational energy release ͑recoil energy͒ distributions are remarkably similar, peaking at very low energy ͑10-20 cm −1 ͒ and decaying in an exponential fashion to approach zero near 300 cm −1 . The average translational energy released is small, shows no dependence on the initial vibrational energy, and spans the range 58-72 cm −1 for the vibrational levels probed. The average value for the seven levels studied is 63 cm −1 . The low fraction of transfer to translation is qualitatively in accord with Ewing's momentum gap model ͓G. E. Ewing, Faraday Discuss. 73, 325 ͑1982͔͒. No evidence is found in the distributions for a high energy tail, although it is likely that the experiment is not sufficiently sensitive to detect a low fraction of transfer at high translational energies. The average translational energy released is lower than has been seen in comparable systems dissociating from triplet and cation states.

A velocity map ion imaging study of difluorobenzene-water complexes: Binding energies and recoil distributions

“…The parameters for the fits to the distributions are given in Table III. As we have observed previously, 11,16 this functional form provides an excellent fit to the data. The three recoil distributions are very similar.…”

“…The S 1 pDFB-Ar recoil distributions are all very similar, so the 3 1 5 1 distribution is representative of this complex. 11 The pDFB-H 2 O distributions are very similar as a group, although clearly different to the Ar case, showing a larger proportion of molecules with higher translational energy release.…”

“…Although the dissociation energy is not known for this case, and hence the excess energy is unknown, it is clearly well above the ϳ1300 cm −1 available for the highest vibrational level we have investigated for pDFB-H 2 O. However, for pDFB-Ar we found that there is essentially no change in the average translational energy released with increasing initial vibrational energy 11 and the limited data set for the water complex also shows no change with increasing vibrational energy. We thus believe it unlikely that the differences arise from the extra vibrational energy available for pyrazine-water.…”

“…The average kinetic energy released to the fragments from each energy level investigated is given in Table IV. As we have found for the pDFB-Ar, pDFB + -Ar, and benzene + -Ar complexes, 11,16,20 most of the energy remains as internal energy of the fragments. There is essentially no change in the average kinetic energy released with increasing available energy.…”

Energy transfer of highly vibrationally excited azulene. II. Photodissociation of azulene-Kr van der Waals clusters at 248 and 266nm

“…[6][7][8][9][10][11][12] Recently, velocity map ion imaging technique and velocity resolved time-of-flight mass spectrometry have been applied to determine the photofragment recoil energy distribution of van der Waals clusters following predissociation. [13][14][15][16][17] In all studies, only the molecules in the electronic excited state were probed. No products can be detected if they are populated in the ground electronic state.…”