| 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: (a) diatomic metal hydrides BeH, MgH, CaH, SrH, ZnH and CdH; (b) linear triatomic metal hydrides BeH2, MgH 2, ZnH2 and HgH2.; Infrared emission spectra of BeH, MgH, CaH, SrH, ZnH and CdH free radicals contained several vibration-rotation bands in their 2Sigma + 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 2Sigma+ states, and correction parameters due to the breakdown of the Born-Oppenheimer approximation were determined. The equilibrium internuclear distances (re) of 9BeH, 24MgH, 40CaH, 88SrH, 64ZnH and 114CdH were determined to be 1.342424(2), 1.729721(1), 2.002360(1), 2.146057(1), 1.593478(2) and 1.760098(3) A, respectively, and the corresponding re distances for 9BeD, 24MgD, 40CaD, 88SrD, 64ZnD and 114CdD are 1.341731(2), 1.729157(1), 2.001462(1), 2.145073(1), 1.593001(2) and 1.759695(2) A, respectively.; Gaseous BeH2, MgH2, ZnH2 and HgH 2 molecules were discovered and unambiguously identified by their high-resolution infrared emission spectra. The nu3 antisymmetric stretching fundamental band and several hot bands in the nu3 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 r0 internuclear distances. For BeH2, ZnH2, ZnD2, HgH2 and HgD 2 molecules, the rotational constants of the 000, 100, 0110 and 001 levels were used to determine the equilibrium rotational constants (Be) and the associated equilibrium intemuclear distances (re). The re distances of ZnH2 and ZnD2 differed by about 0.01%, and those of HgH2 and HgD2 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. |
