The gas phase structure of alpha-pinene, a main biogenic volatile organic compound

The gas phase structure of the bicyclic atmospheric aerosol precursor alpha-pinene was investigated employing a combination of quantum chemical calculation and Fourier transform microwave spectroscopy coupled to a supersonic jet expansion. The very weak rotational spectra of the parent species and all singly substituted C-13 in natural abundance have been identified, from 2 to 20 GHz, and fitted to Watson's Hamiltonian model. The rotational constants were used together with geometrical parameters from density functional theory and ab initio calculations to determine the r(s), r(0), and r(m)((1)) structures of the skeleton, without any structural assumption in the fit concerning the heavy atoms. The double C=C bond was found to belong to a quasiplanar skeleton structure containing 6 carbon atoms. Comparison with solid phase structure is reported. The significant differences of alpha-pinene in gas phase and other gas phase bicyclic monoterpene structures (beta-pinene, nopinone, myrtenal, and bicyclo[ 3.1.1] heptane) are discussed. Published by AIP Publishing.