Absolute intensities of nitric acid overtones

The absolute absorption cross sections for the Delta upsilon = 3 and Delta upsilon = 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) x 10(-8) [2.78 x 10(-8)] and (2.7 +/- 0.3) x 10(-9) [2.14 x 10(-9)]. Scaling the calculated values by 1.15 (the average ratio of measured:calculated) yields predicted oscillator strengths for transitions to upsilon = 5 and upsilon = 6 of 2.9 x 10(-10) and 4.0 x 10(-11), respectively, corresponding to integrated absorption cross sections of 2.6 x 10(-22) and 3.5 x 10(-23) cm(2) molecule(-1) cm(-1), respectively for these transitions. These values are almost 2 times larger than previously estimated.