Alignment of Hg–Ar van der Waals molecule photofragments following photodissociation

Abstract

We have measured the alignment of the photofragments produced by photodissociation of Hg-Ar van der Waals molecules using light around 253.7 nm. The molecules are produced in the X0+ ground state in a supersonic expansion. Tunable laser light close to the Hg 6 'Se-6 3P, transition is then used to excite the molecule to the Bl* state, in which it dissociates. The alignment of the resulting Hg( 3P,) asymptotic atoms is probed by tuning a delayed second laser to the 435.8 nm Hg 6 3P,-7 3S1 atomic transition and monitoring the subsequent fluorescence on the 7 3S1-6 3P2 transition around 546.1 nm. These measurements have been made, we believe for the first time, as a function of dissociating energy from very close to threshold to higher energies. The alignment shows a significant rise with increasing photon energy in line with a semiclassical picture of orbital locking at lower energies and rapid decoupling at higher energies. The results exhibit good agreement with the results of a fully quantum mechanical theory of the system.

A combining rule calculation of the ground state van der Waals potentials of the mercury rare-gas complexes

“…The present D e from the TT model falls in the experimental range from 133.7 to 142.0 cm −1 . The determination of Quayle et al 45 is especially interesting. They started out with the potential of Ref.…”

“…As seen in Table IV, the experimental e = 18.3͑3͒ cm −1 and e e = 0.33͑5͒ cm −1 are actually in very good agreement with the present predictions. It is not clear whether a better analysis with a more realistic potential, similar to what Quayle et al 45 did in the case of Hg-Ar, will resolve the differences in D e and R e .…”

Collision-Induced Fine-Structure Transitions of Hg(63P1 → 63P0) with N2 and CO. 1. Initial Orbital Alignment Effects

“…The purpose of this experiment is to obtain information on molecular state selectivity between the à and B̃ states in the fine-structure process (1) with N 2 and CO. The state selectivity in collisions of excited atoms with rare gases or closed-shell molecules are described as orbital alignment effects of the excited atoms in lots of problems in low-energy atomic collisions. − There are two kinds of experimental methods to elucidate the effects of initial orbital alignment of the excited atoms, i.e., (i) precollision alignment method 11-28 and (ii) half-collision alignment method. − The half-collision method has already been applied to the present fine-structure process with N 2 and CO, ,, and in the present study, we have employed the precollision alignment method to reveal the alignment effect of the atomic orbital of Hg(6 3 P 1 ). We summarize, here, these methods and their a...…”

“…There are two types of situations in the half-collision experiments. In one situation, bound states of stabilized van der Waals (vdW) molecules in supersonic free jets are used as initial states for the photoexcitations, − and in another one, free states of transient collision complex are used under thermal energy conditions in gas cell experiments. − Spectroscopic studies on intramultiplet predissociations of the Hg(6 3 P 1 )−N 2 and Hg(6 3 P 1 )−CO vdW molecules to Hg(6 3 P 0 ) + N 2 and CO have already been reported. , These studies have shown that the predissociation rate of Hg−N 2 in the à state depends on rotational and vibrational quantum numbers and conclude that the overall rotation of the complex and the bending motion (i.e., restricted internal rotation) of N 2 accelerate the predissociation rate. In addition, the average predissociation rates were almost in the same order for both the à and B̃ states.…”