Line Oscillator Strength Measurements in the 0-0 Band of the c′4 1Σu+ ← X 1Σg+ Transition of N2

Oscillator strengths for 48 rotational lines in the 0-0 band of the c1Σ ← X1Σ transition of 14N2, a prominent feature in planetary airglow emissions, have been determined from vacuum ultraviolet photoabsorption spectra recorded with an instrumental resolution of ~ 6.5 × 10-4 nm (resolving power ≈150,000). The sum of the integrated cross sections over all measured lines, including six lines appearing on account of a local perturbation by v = 1 of the b' state, yields a room temperature band f-value of 0.136 ± 0.020. This result is compared with earlier measurements of band-integrated absorption cross sections and with a study of electron-impact-induced emission from c(0), as well as with electron scattering measurements and a nonadiabatic calculation of vibronic band strengths. The relative P- and R-branch absorption intensities deviate systematically from those of an unperturbed 1Σ ← 1Σ band, as expected from the interactions of the c (v = 0) level with nearby Rydberg and valence states. In addition, the variation of the band f-values derived from pairs of R- and P-branch transitions with a common lower-state rotational level, f(J''), are found to be J-dependent, indicating that the f-value obtained from the band-integrated absorption cross section is slightly temperature dependent. The J-dependence of f(J'') is briefly discussed in the context of the interference patterns which characterize the absorption strengths in the region of the widespread interactions between Rydberg and valence state levels