MICROWAVE-SPECTRA, HYPERFINE-STRUCTURE, AND ELECTRIC-DIPOLE MOMENTS FOR CONFORMERS-I AND CONFORMER-II OF GLYCINE

A number of low-J rotational transitions have been measured for two conformations of the simplest amino acid, glycine, providing precise hyperfine transition frequencies and electric dipole moments for radioastronomy searches for glycine in interstellar clouds. Measurements were made between 12 and 25 GHz with a pulsed-nozzle, Fabry-Perot-cavity, Fourier transform microwave spectrometer equipped with either a heated nozzle or laser ablation-nozzle for vaporization of solid phase glycine. Nuclear quadrupole coupling constants were determined for both conformers from measurements of the hyperfine-split rotational transitions. The quadrupole coupling constants for conformer I are eQq(aa) = -1.208(9) MHz and eQq(bb) = -0.343(8) MHz and for conformer II are eQq(aa) = 1.773(2) MHz and eQq(bb) = -3.194(4) MHz. The dipole moment components of both conformers were determined to higher precision. We obtain mu(a) = 3.039(10) X 10(-30) C m [0.911(3)D] and mu(b) = 2.025(17) X 10(-30) C m [0.607(5) D] for conformer I, and mu(a) = 17.92(11) X 10(-30) C m [5.372(34)D] and mu(b) = 3.10(3) X 10(-30) C m [0.93(1)D] for conformer II, where the uncertainties shown are 1 standard deviation.