Double-resonance studies of electronically autoionizing states of molecular nitrogen.

Double-resonance excitation of molecular nitrogen, N2, via selected rotational levels of the , v′ = 0 state has been used to probe the first two bands in the new Ogawa series [M. Ogawa, Can. J. Phys. 42, 1087 (1964)], which lie above the first ionisation threshold of the molecule. These bands are rotationally unresolved in room-temperature and jet-cooled absorption spectra, but the double-resonance technique allows a rotational analysis and first confirmation of the assignment as transitions to n = 4 members of the (A2Πu)ndπ, v Rydberg series. In principle, the probe transition from the , v = 0 level to these Rydberg states corresponds to a two-electron transition, and this aspect of the results is explored. Finally, velocity map imaging allows a determination of the photoelectron branching fractions and angular distributions, providing insight into the electronic autoionisation dynamics. [ABSTRACT FROM AUTHOR]