HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF THE SECOND NEGATIVE SYSTEM OF O$^{+}_{2}$

Abstract

The second negative system ($A^{2}\Pi_{u}-X^{2}\Pi_{g}$) of O$_{2}^{+}$ has been spectroscopically studied for over 70 years}, 685 (1991).} due to the significant role it plays in the chemistry of the upper atmosphere. More recently, the (2,18), (4,20), (6,20),}, 131 (2004).} (3,18), (3,19), and (4,19)}, 81 (2004).} bands were observed in the near infrared. While scanning for N$_{2}^{+}$ lines in a pure helium discharge containing N$_{2}$ as an impurity ($<$8 ppm) for another experiment,} we serendipitously found two new bands of O$^{+}_{2}$, (2,19) and (5,21). The O$^{+}_{2}$ ions were produced in a liquid-nitrogen-cooled positive-column plasma containing 1 Torr of He, where most likely the dominant source of oxygen in the plasma is a small leak in the vacuum system. The spectra were obtained with a Ti:sapphire laser (11,000-13,000 cm$^{-1}$) using velocity modulation, phase modulation with heterodyne detection, noise subtraction, and optical multi-passing. A detailed analysis of the newly observed bands will be presented.