PRESSURE-INDUCED A'' 1SIGMAG+[-X 1SIGMAG+ ABSORPTION IN VACUUM ULTRAVIOLET SPECTRUM OF MOLECULAR NITROGEN

The a″ 1∑+-X 1∑ g+ absorption band of N2, which has been reported recently in a preliminary communication, has been investigated at nitrogen pressures from 10 to 80 torr. A study of the absolute absorption coefficient and of its pressure dependence shows definitely that the observed band arises as a pressureinduced dipole transition at the quoted pressures. The integrated absorption represents an absolute oscillator strength of f/p=3.2×10-8 torr-1. The large bandwidth (400 cm-1) is attributed to the short duration of the dipole-inducing collisions: 1.3×10-14 sec on the average. Thus the observed intensity can be interpreted in terms of an average oscillator strength of f=0.04 per molecule per collision. The apparent optical quadrupole absorption/ value of less than 10-7 corresponds to a very small quadrupole matric element compared to the one which determines the electron excitation cross section. A search for the a″∼X quadrupole emission band in the electron-beam-excited spectrum at very low pressures has resulted in strong evidence for the presence of the 0-0 band of this transition, and tentative assignments of O, Q, and Slines yield approximate values of v0=99 005 cm-1 and B0′= 1.85±0.1S cm-1.