Resonance enhanced multiphoton ionization spectroscopy of the NF molecule: 1,3Φ 3d and 4d Rydberg states

Abstract

The (3dδ)1,3Φ and (4dδ)1,3Φ Rydberg states of NF have been investigated by multiphoton ionization (MPI) spectroscopy. These states were observed as two-photon resonances in an overall (2+1) MPI process from NF a1Δ produced from the F+N3 reaction. Ab initio calculations performed at the multireference double excitation configuration interaction level showed that the excited Φ states were of Rydberg character with configurations of ...1π45σ22π1(3dδ)1 and ...1π45σ22π1(4dδ)1. The 3Φ←a1Δ two-photon transitions were found to derive their intensities from spin–orbit and spin-uncoupling interactions in the 1Φ3, 3Φ4, 3Φ3, and 3Φ2 upper states. Analysis of the rotationally resolved bands, using a model which includes these factors, allowed the spin–orbit constant, aπ, for the 2π valence orbital to be derived as (159.0±1.0) cm−1. Rotationally resolved envelopes recorded for the (3dδ)1Φ, v′=0, 1←a1Δ, v″=0 and (3pπ)1Σ+, v′=0←a1Δ, v″=0 (2+1) NF MPI bands, could be simulated reasonably well assuming a Boltzmann rotational distribution for the a 1Δ state at ≊180 K. Experiments showed, however, that this was not a true measure of the initial state distribution because of predissociation or perturbation effects in the resonant intermediate state. Assignments for other two-photon resonant NF MPI bands observed in this work are also suggested.