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

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.