Mid-Infrared Signatures of Hydroxyl Containing Water Clusters: Infrared Laser Stark Spectroscopy of OH-H2O and OH(D2O)n (n=1-3)

F. HERNÁNDEZ; J. T. BRICE; C. M. LEAVITT; T. LIANG; P. RASTON; G. A. PINO; G. E. DOUBERLY

JOURNAL OF CHEMICAL PHYSICS

AMER INST PHYSICS

Lugar: Melville; Año: 2015 vol. 143 p. 1643041 - 16430412

0021-9606

Small water clusters containing a single hydroxyl radical are synthesized in liquid heliumdroplets. The OHH2O and OH(D2O)n clusters (𝑛 = 1 − 3) are probed with infrared laserspectroscopy in the vicinity of the hydroxyl radical OH stretch vibration. Experimental bandorigins are qualitatively consistent with ab initio calculations of the global minimum structures;however, frequency shifts from isolated OH are significantly over-predicted by both B3LYP andMP2 methods. An effective Hamiltonian that accounts for partial quenching of electronicangular momentum is used to analyze Stark spectra of the OHH2O and OHD2O binarycomplexes, revealing a 3.70(5) Debye permanent electric dipole moment. Computations of thedipole moment are in good agreement with experiment when large-amplitude vibrationalaveraging is taken into account. Polarization spectroscopy is employed to characterize twovibrational bands assigned to OH(D2O)2, revealing two nearly isoenergetic cyclic isomers thatdiffer in the orientation of the non-hydrogen-bonded deuterium atoms relative to the plane of thethree oxygen atoms. The dipole moments for these clusters are determined to be approximately2.5 and 1.8 Debye for ?up-up? and ?up-down? structures, respectively. Hydroxyl stretching bandsof larger clusters containing three or more D2O molecules are observed shifted approximately300 cm1 to the red of the isolated OH radical. Pressure dependence studies and ab initiocalculations imply the presence of multiple cyclic isomers of OH(D2O)3.