Absolute Intensities of Nitric Acid Overtones

Abstract

The absolute absorption cross sections for the Δv = 3 and Δv = 4 OH local mode transitions in room-temperature, gas-phase nitric acid have been measured and calculated ab initio. The measured [calculated at the QCISD/6-31+G(d,p) level] oscillator strengths are (2.9 ± 0.3) × 10-8 [2.78 × 10-8] and (2.7 ± 0.3) × 10-9 [2.14 × 10-9]. Scaling the calculated values by 1.15 (the average ratio of measured:calculated) yields predicted oscillator strengths for transitions to v = 5 and v = 6 of 2.9 × 10-10 and 4.0 × 10-11, respectively, corresponding to integrated absorption cross sections of 2.6 × 10-22 and 3.5 × 10-23 cm2 molecule-1 cm-1, respectively for these transitions. These values are almost 2 times larger than previously estimated.