Photoionization of excited molecular states using multiphoton excitation techniques

Photoelectron spectra are reported for three photon resonant, four photon ionization of H2 via the B 1Σ/sub u/+, v = 7 (J = 2,4) and C 1π/sub u'/, v = 0-4 (J = 1) levels and of N2 via the o31π/sub u'/, v = 1,2, b 1π/sub u'/, v = 3-5, and c 1π/sub u'/, v = 0 levels. The results reflect both the spectroscopy and the dynamics of photoionization of excited molecular states and are discussed in terms of the selection rules for photoionization and the relative probabilities of photoionization from Rydberg and valence states. In some cases, in accordance with the Franck-Condon principle, the results demonstrate that resonant multiphoton ionization through Rydberg states may be a powerful technique for the production of electronic, vibrational, and rotational state selected ions. However, in other cases, systematic departures from Franck-Condon factors are observed, which reflect the more subtle dynamics of excited state photoionization. 23 references, 6 figures, 2 tables