PNNL

Abstract

The microwave spectrum of n-butyl nitrate was recorded in the 5 to 20 GHz frequency range using chirped-pulsed and cavity-based molecular jet Fourier transform microwave spectrometers. A quantum chemistry structural analysis yielded thirteen stable conformers, among them the five most energetically stable ones were observed in the experimental spectrum. The most stable conformer features a butyl chain with an anti-gauche-anti conformation (AGA) where the ?-carbon atom is about 63° out of the nitrate plane. For this conformer, spectra of all 13C and 15N minor isotopologues could be measured, and a semiexperimental equilibrium structure was determined and compared to the equilibrium structure obtained from geometry optimizations. The conformer with a straight butyl chain (AAA), and three other conformers (GAA, GGA and AGG) were also observed. Accurate rotational constants, centrifugal distortion constants, and 14N nuclear quadrupole coupling constants could be deduced and compared to the theoretical values.