Zwitter Ionization of Glycine at Outer Space Conditions due to Microhydration by Six Water Molecules

We investigate glycine microsolvation with water molecules, mimicking astrophysical conditions, in our laboratory by embedding these clusters in helium nanodroplets at 0.37 K. We recorded mass selective infrared spectra in the frequency range 1500-1800  cm^{-1} where two bands centered at 1630 and 1724  cm^{-1} were observed. By comparison with the extensive accompanying calculations, the band at 1630  cm^{-1} was assigned to the COO^{-} asymmetric stretching mode of the zwitter ion and the band at 1724  cm^{-1} was assigned to redshifted C=O stretch within neutral clusters. We show that zwitter ion formation of amino acids readily occurs with only few water molecules available even under extreme conditions.