RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTROSCOPY OF THE NF MOLECULE - (1)SIGMA(+) AND (1)DELTA 3P RYDBERG STATES

Two Rydberg states of the NF molecule, the 2 1DELTA and 2 1SIGMA+ stat es, have been investigated by multiphoton ionization (MPI) spectroscop y. These states are observed via the two-photon resonance enhancements they provide in the multiphoton ionization spectra of NF a 1DELTA and NF b 1SIGMA+. Both states are assigned on the basis of experimental e vidence as Rydberg states with the dominant configuration ...1pi(4)5si gma(2)2pi1 (3ppi)1. Ab initio calculations performed at the multirefer ence determinant configuration interaction (MRDCI) level showed that t hese states were of mixed Rydberg-valence character with the Rydberg c haracter [...1pi(4)5sigma(2)2pi1 (3ppi)1] dominating at short bond len gths (< 1.35 angstrom) and the valence character (...1pi(3)5sigma(2)2p i3) becoming more important at longer bond lengths (> 1.35 angstrom). These calculations also proved useful in providing a mechanism to acco unt for the rotational predissociation observed in the experimental sp ectra.