Photophysics of O-2 excited by tunable laser radiation around 193 nm

The photodissociation/ionization dynamics of O-2 around 193 nm have been st udied using a narrowband tunable ArF excimer laser and the velocity map ima ging technique. Angular and kinetic energy distributions of the product Oions and O(P-3(2)) atoms are recorded and analyzed. The production of O(P-3 (2)) atoms is resonance enhanced on the one-photon level by the B (3)Sigma( u)(-)(v=4) state, which is part of the B (3)Sigma(u)(-)<-- X (3)Sigma(g)(-) Schumann-Runge bands. Angular distribution measurements for individual rot ational levels of the B state yield values for the anisotropy parameter, be ta(SR), which are in good agreement with the values predicted by independen t measurements of predissociation lifetimes from spectral linewidths. An av erage value of beta=0.48 is found for the underlying Herzberg continuum at 193 nm. O-2(+) production is enhanced on the two-photon level via members o f the ns sigma(g)(n-1)d pi(g)(1)Sigma(g)(+) Rydberg series terminating at h igher vibrational levels of the ion. The high Rydberg states autoionize int o the O-2(+) X (2)Pi(g) ground state or absorb one more photon and then aut oionize into the A (2)Pi(u) and b (4)Sigma(u)(-) states of O-2(+), which su bsequently fluoresce. Production of O+ from one- and two-photon dissociatio n of the O-2(+) formed after two-photon absorption is also observed and cha racterized. (C) 2000 American Institute of Physics. [S0021-9606(00)01709-8] .