Line Oscillator Strength Measurements in the 0 È 0 Band Of

Oscillator strengths for 48 rotational lines in the 0È0 band of the transition of a c4@ 1&u`^X1&g` 14N2, prominent feature in planetary airglow emissions, have been determined from vacuum ultraviolet photoabsorption spectra recorded with an instrumental resolution of D6.5] 10~4 nm (resolving power B150,000). 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 as well as with electron c4@ (0), scattering measurements and a nonadiabatic calculation of vibronic band strengths. The relative Pand R-branch absorption intensities deviate systematically from those of an unperturbed 1&^ 1& band, as expected from the interactions of the (v\ 0) level with nearby Rydberg and valence states. In c4@ addition, the variation of the band f-values derived from pairs of Rand 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 brieÑy 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. Subject headings : ISM: molecules È molecular data È planets and satellites : general È ultraviolet : general