Infrared Spectra of Isotopic Nitrous Acids

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Abstract
The infrared spectra of isotopic cis‐ and trans‐nitrous acid molecules including the 15N and D species have been obtained in the vapor and solid phases. All fundamentals of the normal cis and trans isomers have been identified, and previous assignments of two modes have been revised. From the isotopic frequencies of the torsion fundamental and the temperature dependence of two pairs of fundamentals, the potential‐energy minimum of the cis isomer was deduced to be 0.39±1.0 kcal/mole above that of the trans isomer. The torsion barrier above the trans‐isomer minimum was calculated to be 11.57±0.2 kcal/mole. Valence force constants for the cis and trans nitrous acids have been derived also. These constants reproduced the experimental 18O frequencies reasonably well.