Determination of absolute strengths of N2 quadrupole lines from high‐resolution ground‐based IR solar observations

Abstract

High‐resolution, high signal‐to‐noise ratio, solar absorption spectra recorded with a Fourier transform spectrometer at the International Scientific Station of the Jungfraujoch, Switzerland, have been analyzed to determine the strengths of several lines belonging to the S branch of the N2 (1–0) electric quadrupole vibration‐rotation band centered at 2329.9168 cm−1. The method which was applied here was based on equivalent width measurements of lines observed over a broad range of air masses; extrapolation of these measurements to zero air mass gave the line strengths for the transitions S7 to, S10, independent of half widths, an ambiguity unavoidable with the use of curve‐fitting techniques. The resulting absolute accuracies of the line strengths derived here, estimated to be better than ±2.5% for S8, ±2.6% for S10, ±3.4% for S9, and ±5.1% for S7, are due largely to the high quality and quantity of the spectra retained in this analysis and the accuracy with which the observation conditions are known. An important application of the improved values for these N2 transitions, which have low initial ground state energies, is the direct determination of the line‐of‐sight atmospheric air masses associated with remotely sensed infrared spectroscopic observations. Positions of the N2 transitions studied here have further been redetermined with an absolute accuracy better than 0.0002 cm−1.