Microwave Spectrum and Structure of Nitric Acid

Abstract

The microwave spectra of five further isotopic species of nitric acid, H18ONO2, cis-HON18OO, trans-HONO18O, cis-HO15N18OO, and D15NO3, have been investigated. The data have been used to refine the previous structural determination of Millen and Morton. In the calculation of structure, particular consideration has been given to the use of ground-state moments of inertia in Kraitchman's equations for near-oblate planar molecules. The structure was calculated using several different methods, including the double-substitution method due to Pierce, in order to substantiate the following structural parameters: O–H=0.964, (H)O–N=1.406, cis–N–O=1.211, trans-N–O=1.199 Å, ∠HON=102°9′, ∠cis-ONO=115°53′, ∠trans-ONO=113°51′, and O···O (NO2 group)=2.184 Å. This determination clearly demonstrates a 2° tilt of the NO2 group away from the hydrogen atom. The NO2 parameters are close to those found in a number of related molecules, but there is some evidence that the cis-NO bond in HNO3 is slightly longer than the trans-NO bond. The NOH configuration is very similar to that found in formaldoxime. Further evidence for the exact planarity of nitric acid is given. Stark-effect measurements limit the out-of-plane component of the dipole moment μC to a value less than 1.1×10−3 D. The other components have been redetermined to have the values μA=1.99 D and μB=0.88 D, giving a total dipole moment μ=2.17±0.02 D.

An ab initio and dynamics study of the photodissociation of nitric acid HNO3

“…The calculations of the PESs were carried out with the COLUMBUS program package [10] at the CASSCF level of theory in conjunction with the DALTON suite programs [11] using an optimized planar ground state geometry of with the geometry determined by microwave spectroscopy [12]. The ground state consists of 13 a' and 3 a" occupied molecular orbitals.…”

Rotational spectroscopy and dipole moment of cis-cis HOONO and DOONO

“…25,26 However, the inertial defect is a balance of in-plane ͑typically positive͒ and out-of-plane ͑typically negative͒ contributions. The inertial defect for HOONO is smaller than that for HONO 2 , 29 indicating more contribution in HOONO from all out-of-plane motions. Cox and Riveros 29 measured inertial defects for a series of nitric acid isotopomers and found the largest change in inertial defect ͑−0.0089 amu Å 2 ͒ with deuterium substitution.…”

The rotational spectra of the 61, 71, 81, 91 and 51/92 vibrational states of H15NO3

“…Nitric acid is a planar oblate asymmetric rotor (j = 0.729) belonging to the C s point group with dipole moments of l a = 1.986D and l b = 0.882D [18]. The spectrum of each vibrational state is characterized by strong R-type band heads spaced by approximately 12.5 GHz throughout the spectrum along with much more broadly spaced Q-branch transitions.…”