High-resolution infrared emission spectroscopy of diatomic and triatomic metal hydrides
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Date
2006
Authors
Shayesteh, Alireza
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Several hydrides of Group 2 and 12 elements were generated in the gas phase using an emission source that combines an electrical discharge with a high temperature furnace, and their high-resolution infrared emission spectra were recorded with a Fourier transform spectrometer. Two classes of molecules were studied: <em>a)</em> diatomic metal hydrides BeH, MgH, CaH, SrH, ZnH and CdH; <em>b)</em> linear triatomic metal hydrides BeH<sub>2</sub>, MgH<sub>2</sub>, ZnH<sub>2</sub> and HgH<sub>2</sub>. <br /><br /> Infrared emission spectra of BeH, MgH, CaH, SrH, ZnH and CdH free radicals contained several vibration-rotation bands in their <sup>2</sup>SIGMA<sup>+</sup> ground electronic state. The new data were combined with all the previous ground state data from diode laser infrared spectra and pure rotation spectra available in the literature. Spectroscopic constants, i. e. , vibrational band origins, rotational, centrifugal distortion, and spin-rotation interaction constants, were determined for each observed vibrational level by least-squares fitting of all the data. In addition, the data from all isotopologues were fitted simultaneously using the empirical Dunham-type energy level expression for <sup>2</sup>SIGMA<sup>+</sup> states, and correction parameters due to the breakdown of the Born-Oppenheimer approximation were determined. The equilibrium internuclear distances (<em>r</em><sub>e</sub>) of <sup>9</sup>BeH, <sup>24</sup>MgH, <sup>40</sup>CaH, <sup>88</sup>SrH, <sup>64</sup>ZnH and <sup>114</sup>CdH were determined to be 1. 342424(2), 1. 729721(1), 2. 002360(1), 2. 146057(1), 1. 593478(2) and 1. 760098(3) angstroms, respectively, and the corresponding <em>r</em><sup>e</sup> distances for <sup>9</sup>BeD, <sup>24</sup>MgD, <sup>40</sup>CaD, <sup>88</sup>SrD, <sup>64</sup>ZnD and <sup>114</sup>CdD are 1. 341731(2), 1. 729157(1), 2. 001462(1), 2. 145073(1), 1. 593001(2) and 1. 759695(2) angstroms, respectively. <br /><br /> Gaseous BeH<sup>2</sup>, MgH<sup>2</sup>, ZnH<sup>2</sup> and HgH<sup>2</sup> molecules were discovered and unambiguously identified by their high-resolution infrared emission spectra. The ν<sub>3</sub> antisymmetric stretching fundamental band and several hot bands in the ν<sub>3</sub> region were rotationally analyzed, and spectroscopic constants were obtained for almost all naturally-occurring isotopologues. The rotational constants of the 000 ground states were used to determine the <em>r</em><sub>0</sub> internuclear distances. For BeH<sub>2</sub>, ZnH<sub>2</sub>, ZnD<sub>2</sub>, HgH<sub>2</sub> and HgD<sub>2</sub> molecules, the rotational constants of the 000, 100, 01<sup>1</sup>0 and 001 levels were used to determine the equilibrium rotational constants (<em>B</em><sub>e</sub>) and the associated equilibrium internuclear distances <em>r</em><sub>e</sub>. The <em>r</em><sub>e</sub> distances of ZnH<sub>2</sub> and ZnD<sub>2</sub> differed by about 0. 01%, and those of HgH<sub>2</sub> and HgD<sub>2</sub> differed by about 0. 005%. These discrepancies were larger than the statistical uncertainties by one order of magnitude, and were attributed to the breakdown of the Born-Oppenheimer approximation.
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Keywords
Chemistry, Infrared emission spectra, Gaseous metal hydrides, Group 2 and 12 elements, BeH, MgH, CaH, SrH, ZnH, CdH, BeH2, MgH2, ZnH2, HgH2