Nonadiabatic effects in the photodetachment of ClH2−

Low frequency vibrational anharmonicity and nuclear spin effects of Cl-(H2) and Cl-(D2)

Low frequency combination bands of ³⁵Cl^-(H₂) and ³⁵Cl^-(D₂) have been measured in the region between 600 and 1100 cm^-1 by infrared predissociation spectroscopy in a cryogenic 22-pole ion trap using a free electron laser at the FELIX Laboratory as a tunable light source. The ³⁵Cl^-(H₂) (³⁵Cl^-(D₂)) spectrum contains three bands at 773 cm^-1 (620 cm^-1), 889 cm^-1 (692 cm^-1), and 978 cm^-1 (750 cm^-1) with decreasing intensity toward higher photon energies. Comparison of the experimentally determined transition frequencies with anharmonic vibrational self-consistent field and vibrational configuration interaction calculations suggests the assignment of the combination bands v₁ + v₂, 2v₁ + v₂, and 3v₁ + v₂ for ³⁵Cl^-(H₂) and 2v₁ + v₂, 3v₁ + v₂, and 4v₁ + v₂ for ³⁵Cl^-(D₂), where v₁ is the ³⁵Cl^-⋯H₂ stretching fundamental and v₂ is the Cl^-(H₂) bend. The observed asymmetric temperature dependent line shape of the v₁ + v₂ transition can be modeled by a series of ∑⁺-∏ ro-vibrational transitions, when substantially decreasing the rotational constant in the vibrationally excited state by 35%. The spectrum of ³⁵Cl^-(D₂) shows a splitting of 7 cm^-1 for the strongest band which can be attributed to the tunneling of the ortho/para states of D₂.

Spin-orbit quenching of Cl(2P(1∕2)) by H2

We report fully-quantum, time-independent, scattering calculations for the spin-orbit quenching of Cl((2)P(1∕2)) by H(2) molecules at low and moderate temperature. Our calculations take into account chemical reaction channels. Cross sections are calculated for total energies up to 5000 cm(-1) which are used to determine, by thermal averaging, state-to-state rate coefficients at temperatures ranging from 50 to 500 K. Spin-orbit relaxation of chlorine is dominated by collisions with H(2) in the rotationally excited states j = 2 and j = 3. In the former case the near-resonant energy transfer is the primary relaxation mechanism. The inclusion of the reactive channel could lead differences compared to pure inelastic calculations. Good agreement is obtained with experimental relaxation measurements at room temperature.

Dynamical regimes on the Cl + H2 collisions: inelastic rainbow scattering

While Cl + H(2) reactive collisions have been a subject of numerous experimental and theoretical studies, inelastic collisions leading to rotational energy transfer and/or vibrational excitation have been largely ignored. In this work, extensive quantum mechanical calculations covering the 0.5-1.5 eV total energy range and various initial rovibrational states have been carried out and used to perform a joint study of inelastic and reactive Cl + H(2) collisions. Quasiclassical trajectories calculations complement the quantum mechanical results. The analysis of the inelastic transition probabilities has revealed the existence of two distinct dynamical regimes that correlate with low and high impact parameters, b, and are neatly separated by glory scattering. It has been found that while high-b collisions are mainly responsible for |Δj| = 2 transitions which dominate the inelastic scattering, they are very inefficient in promoting higher |Δj| transitions. The effectiveness of this type of collision also drops with rotational excitation of H(2). In contrast, reactive scattering, that competes with |Δj| > 2 inelastic transitions, is exclusively caused by low-b collisions, and it is greatly favored when the reactants get rotationally excited. Previous studies focusing on the reactivity of the Cl + H(2) system established that the van der Waals well located in the entrance channel play a key role in determining the mechanism of the collisions. Our results prove this to be also a case for inelastic processes, where the origin of the double dynamical regime can be traced back to the influence exerted by this well that shapes the topology of the entrance channel of the Cl-H(2) system.

Slow electron velocity-map imaging of negative ions: applications to spectroscopy and dynamics

Anion photoelectron spectroscopy (PES) has become one of the most versatile techniques in chemical physics. This article briefly reviews the history of anion PES and some of its applications. It describes efforts to improve the resolution of this technique, including anion zero electron kinetic energy (ZEKE) and the recently developed method of slow electron velocity-map imaging (SEVI). Applications of SEVI to studies of vibronic coupling in open-shell systems and the spectroscopy of prereactive van der Waals complexes are then discussed.