Lifetime of low vibrational levels of the metastableB̃2B2state ofH2O+<

Abstract

The decay of metastable states of the water radical cation H 2 O + has been observed in an experiment that combines photofragment momentum imaging and electrostatic ion-beam trapping in a crossed-beam geometry. Photoabsorption of 532-nm laser light from a fast beam of H 2 O + is observed to yield fragmentation into both OH 0 + H + and OH + + H 0 . Using coincident photofragment momentum imaging, the initial state of the observed photofragmentation is associated with low vibrational levels of the second excitedB 2 B 2 state of H 2 O + , dissociating via absorption onto a repulsive part of theà 2 A 1 state. Electrostatic ion trapping in the laser interaction region is used to follow the photofragment intensity as a function of time and to determine the lifetime of the metastable states to be τB 2 B 2 = 198 ± 11 μs.

Nonadiabatic Quantum Dynamics Predissociation of H2O+(B̃ 2B2)

“…Recently, Harbo et al 22 performed photoabsortion experiments to measure the lifetime of we have carried out multireference configuration interaction calculations in the C s symmetry with 7 valence electrons in (7a',1a") orbitals obtained from CASSCF calculations in a space of (10a',1a") orbitals constructed using the aug-cc-pvqz basis set for oxygen and aug-cc-pvtz for hydrogen atoms.…”

Nonadiabatic fragmentation of H2O+ and isotopomers. Wave packet propagation using ab initio wavefunctions

“…In contrast with the experiment of Tan et al, 12 where the fragmentation of H 2 O + (B) ions is recorded just after their formation, in the experiment of Harbo et al, 25 the H 2 O + ions produced by the ionization of H 2 O are stored for a relatively long time; most of the ions undergo fragmentation and only those with an energy below the dissociation threshold survive and are, afterwards, irradiated with a 532 nm (2.33 eV) laser, and the ensuing fragmentation branching ratios measured. The B state only holds two vibrational states below the lowest asymptotic energy of state X and the observed fragmentation was explained as due to the photodissociation of these metastable vibrational states of B.…”

“…In the (e-2e) + (e-e + ion) experiments of Tan et al, 12 the ionization of H 2 O is fast enough, compared to the characteristic rotational and vibrational periods of the molecule, that one can assume that the initial H 2 O + wave packet is obtained by a FC transition from the ground state of H 2 O. In this work, we also address the photodissociation experiments of Harbo et al, 25 where the fragmentation starts from specific excited vibrational levels in H 2 O + (B). These authors carried out a crossed-beam experiment, where a H 2 O + beam was crossed by a 532 nm laser.…”

“…To simulate the experimental 25 conditions, we have timepropagated an initial wave packet that corresponds to the vibrational eigenfunction whose energy lies 2.33 eV above the vibrational ground state in the adiabatic B surface. This vibrational state, whose probability density is shown in Fig.…”

Coincidence spectroscopy: Past, present and perspectives

“…As the neutral particles are considerably more difficult to steer than their charged counterparts, the method of handling such an experiment can be two fold: i) the product of the ionization process is accelerated towards a detector by means of an electric lens, in the assumption that it will fragment subsequent to the extraction, and, based on the difference in the flight time of the end-products, it is discriminated between the charged and neutral particles (as reported by Martin et [73]). The latter approach has the advantage that it is well suited for investigating decay processes in which the emission of neutrals takes place in the first step of the fission.…”