High-resolution jet absorption study of nitrogen near 800 Å

Abstract

The absorption spectrum of a supersonic free jet expansion of 14N2 in He has been photographically recorded in the region of the He continuum from ∼900 to 650 Å at reciprocal dispersions of 0.26 and 0.19 Å/mm. The low rotational temperature of close to 20 K results in a drastic simplification of the band structures compared to room or even liquid nitrogen temperature spectra. This report concentrates on the region from 835 to 790 Å and presents a survey of vibronic structures up to the first ionization potential. The Rydberg series of np complexes converging to v=0 in the ground state X 2Σ+g of the ion can be followed to n=39, the low-J rotational structure being clearly discernible in complexes as high as n=19. The application of multichannel quantum defect theory to a least-squares analysis of four series of rovibronic levels associated with the lowest rotational levels N+=0, 1, and 2 of the ion leads to very substantially reduced error limits for the ionization potential of 14N2 and reveals a number of irregularities that point to perturbations by Rydberg levels derived from A 2Πu of N+2.