A co-axially configured submillimeter spectrometer and investigations of hydrogen bound molecular complexes

摘要

The development of a co-axially configured submillimeter spectrometer isreported. The spectrometer has been constructed to observe molecular complexes thatexhibit non-covalent interactions with energies much less than that of a traditionalcovalent bond. The structure of molecular complexes such as those formed between arare gas and a hydrogen halide, Rg:HX where Rg is a rare gas (Rg=Ne, Ar and Kr) andHX (X=F, Cl, Br and I) can be determined directly and accurately. The center of massinteraction distance, RCM, as well as the angle of the hydrogen halide is determined,along with direct evaluation of the intermolecular vibrations as well as accurateisomerization energies between the hydrogen bound and van der Waals forms. Theaccuracy of the frequency determination of rovibrational transitions using thesubmillimeter spectrometer is also evaluated by direct comparison with the state-of-theartpulsed nozzle Fourier transform microwave spectrometer, and this accuracy isestimated to be less than 1 kHz at 300 GHz.The tunneling or geared bending vibration of a dimer of hydrogen bromide orhydrogen iodide has been investigated. The selection rules, nuclear statistics and intensity alternation for transitions observed in these dimmers, which is a consequenceof interchanging two identical nuclei in the low frequency geared bending vibration ofthe molecular complex, are reported. Furthermore, the rotation and quadrupole couplingconstants are used to determine a vibrationally averaged structure of the complex. Theenergy of the low frequency bending vibration can then be compared with ab initiobased potential energy surfaces.A study of the multiple isomeric forms of the molecular complex OC:HI is alsopresented. Multiple isotopic substitutions are used to determine the relevant ground statestructures and data reported evidence for an anomalous isotope effect supporting aground state isotopic isomerization effect.All spectroscopic data that has been reported here has been additionally used tosubsequently model and generate vibrationally complete morphed potential energysurfaces that are capable or reproducing the experimentally observed data. The utility ofthis procedure is evaluated on a predicative basis and comparisons made with newlyobserved data.