# THE DISCOVERY OF BRIDGED HPSI BY ROTATIONAL SPECTROSCOPY

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 Title: THE DISCOVERY OF BRIDGED HPSI BY ROTATIONAL SPECTROSCOPY Creators: McCarthy, M. C.; Lattanzi, V.; Thaddeus, P.; Halfen, D. T.; Ziurys, L. M.; Thorwirth, Sven; Gauss, J. Issue Date: 2009 Publisher: Ohio State University Abstract: The pure rotational spectrum of bridged HPSi, the isomer calculated to be the global minimum of the [H,Si,P] potential energy surface, has been measured using a combination of Fourier transform microwave spectroscopy (FTM) and millimeter/submillimeter direct absorption techniques. In the centimeter-wave band, the lowest two $a$-type rotational transitions in the $K_a = 0$ ladder were measured for the normal isotopic species, HP$^{29}$Si, HP$^{30}$Si, and DPSi in a supersonic molecular beam discharge source using a dilute mixture of SiH$_4$ (or SiD$_4$) and PH$_3$. The experimental work was initially guided by theoretical structures and rotational constants obtained at the CCSD(T)/cc-pwCVQZ level of theory and zero-point vibrational corrections at the CCSD(T)/cc-pV(T+$d$)Z level. Following detection of HPSi in the FTM experiment, theoretical best estimates for the structure and the rotational constants were obtained using additivity and extrapolation techniques. \vspace{1em} On the basis of the centimeter-wave data, the millimeter/submillimeter spectrum of normal HPSi was subsequently measured between 287 and 421 GHz, including K$_a$ components from K$_a$ = 0 to 5, using a combination of gas-phase elemental phosphorus, H$_2$, and SiH$_4$ diluted in argon through an AC glow discharge. From the combined data set, precise spectroscopic constants have been determined using a standard asymmetric top Hamiltonian; all of the measured constants are in excellent agreement with those predicted from theory. From the available data, an unusual H-bridged structure has been derived in which the H atom is situated slightly closer to the P atom. The geometry of HPSi is in remarkable contrast to that of the C and/or N anaogues, i.e. HCN/HNC, HCP, and HNSi which are all linear. Description: Author Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden St.; Cambridge, MA 02138, and School of Engineering \& Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138; Department of Chemistry, Department of Astronomy, and Steward Observatory, University of Arizona, Tucson, AZ, 85721; Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany; Institut fur Physikalische Chemie, Johannes Gutenberg-Universitat Mainz, Jakob-Welder-Weg 11, 55128 Mainz, Germany URI: http://hdl.handle.net/1811/38190 Other Identifiers: 2009-RC-01