Articles you may be interested inCommunication: Vacuum ultraviolet laser photodissociation studies of small molecules by the vacuum ultraviolet laser photoionization time-sliced velocity-mapped ion imaging method J. Chem. Phys. 135, 071101 (2011); 10.1063/1.3626867 Photodissociation dynamics of 3-bromo-1,1,1-trifluoro-2-propanol and 2-(bromomethyl) hexafluoro-2-propanol at 234 nm: Resonance-enhanced multiphoton ionization detection of Br (2 P j ) Photodissociation and photoionization of 2,5-dihydroxybenzoic acid at 193 and 355 nm J. Chem. Phys. 133, 244309 (2010); 10.1063/1.3518709 Br ( P j 2 ) atom formation dynamics in ultraviolet photodissociation of tert-butyl bromide and iso-butyl bromideThe photodissociation dynamics of diiodomethane molecules has been investigated in the wavelength range of 277-305 nm by an ion imaging spectrometer operated under optimal conditions for velocity mapping, where the ions were generated from ͑2ϩ1͒ multiphoton ionization of I( 2 P 3/2 ) and I*( 2 P 1/2 ) fragments with the same laser as that to dissociate the parent molecules. The speed and angular distributions of I* and I fragments were determined from the images. The translational energy distribution of I*( 2 P 1/2 ) fragment consists of a single Gaussian component ͑named G*͒, while that of I( 2 P 3/2 ) consists of two Gaussian components ͑named G1 and G2͒. It was found that the component G* and G2 show similar angular distributions and similar fragmentation energy partitioning ratios, indicating that these two components originate from dissociation at the same electronically excited state, while the component G1 is from another state. Three fragmentation pathways were employed to account for the experimental observations, the adiabatic dissociation from the 1B 1 state to form I( 2 P 3/2 ) with component G1, the adiabatic dissociation from the 2B 1 state to form I*( 2 P 1/2 ) with component G*, and the nonadiabatic dissociation from the 2B 1 state caused by coupling with the higher 2A 1 state to form I( 2 P 3/2 ) with component G2.
Employing a high-resolution (velocity resolution deltanu/nu<1.5%) time-sliced ion velocity imaging apparatus, we have examined the photodissociation of CH2BrCl in the photon energy range of 448.6-618.5 kJ/mol (193.3-266.6 nm). Precise translational and angular distributions for the dominant Br(2P32) and Br(2P12) channels have been determined from the ion images observed for Br(2P32) and Br(2P12). In confirmation with the previous studies, the kinetic-energy distributions for the Br(2P12) channel are found to fit well with one Gaussian function, whereas the kinetic- energy distributions for the Br(2P32) channel exhibit bimodal structures and can be decomposed into a slow and a fast Gaussian component. The observed kinetic-energy distributions are consistent with the conclusion that the formation of the Br(2P32) and Br(2P12) channels takes place on a repulsive potential-energy surface, resulting in a significant fraction (0.40-0.47) of available energy to appear as translational energy for the photo fragments. On the basis of the detailed kinetic-energy distributions and anisotropy parameters obtained in the present study, together with the specific features and relative absorption cross sections of the excited 2A', 1A", 3A', 4A', and 2A" states estimated in previous studies, we have rationalized the dissociation pathways of CH2BrCl in the A-band, leading to the formation of the Br(2P32) and Br(2P12) channels. The analysis of the ion images observed at 235 nm for Cl(2P(32,12)) provides strong evidence that the formation of Cl mainly arises from the secondary photodissociation process CH2Cl + hnu --> CH2 + Cl.
Neutral atoms have been observed to survive intense laser pulses in high Rydberg states with surprisingly large probability. Only with this Rydberg-state excitation (RSE) included is the picture of intense-laser-atom interaction complete. Various mechanisms have been proposed to explain the underlying physics. However, neither one can explain all the features observed in experiments and in time-dependent Schrödinger equation (TDSE) simulations. Here we propose a fully quantummechanical model based on the strong-field approximation (SFA). It well reproduces the intensity dependence of RSE obtained by the TDSE, which exhibits a series of modulated peaks. They are due to recapture of the liberated electron and the fact that the pertinent probability strongly depends on the position and the parity of the Rydberg state. We also present measurements of RSE in xenon at 800 nm, which display the peak structure consistent with the calculations.PACS numbers:
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