Laser spectroscopy, matrix isolation and ab initio studies of free radicals and weakly bound complexes.
thesisposted on 19.11.2015, 08:48 by Peter Robert. Butler
The work presented in this thesis applies laser spectroscopy, matrix isolation and ab initio calculations to the study of free radicals and weakly bound species. The C - X region of BaOH has been re-investigated in the gas phase at higher resolution than by previous workers. A new assignment of the recorded spectra is tentatively proposed based on the higher resolution achieved. The spectrum appears to be heavily perturbed, which seriously complicates the spectral assignment. A new basis set extrapolation procedure has been developed for ab initio calculations on van der Waals complexes. The procedure developed, a modification of the Truhlar extrapolation, employs calculations using modest sized basis sets. This has been tested on 15 van der Waals species with well known equilibrium dissociation energies and bond distances. The modified Truhlar extrapolation procedure is found to be generally of comparative accuracy to CCSD(T)/aug-cc-pV5Z calculations but at much reduced computational cost. The modified Truhlar extrapolation has been applied for the first time to HRgF molecules, where Rg is Ar, Ne and He. The potential energy surfaces generated for HHeF and HNeF represent the most accurate ab initio calculations to date on these species. The HArF calculations are of comparable accuracy to aug-cc-pV5Z calculations by other workers. Vibrational frequencies have also been calculated for all three molecules. The modified Truhlar extrapolation procedure has been applied for the first time to RgC2 clusters, where Rg is Ar, Ne and He. The potential energy surfaces generated. Rovibrational frequencies have been calculated for all three clusters. These lead to the conclusion that both ArC2 and NeC2 are spectroscopically observable, although this would be challenging. Matrix isolation apparatus recently built for recording LIF spectra of trapped reactive intermediates has been tested, improved and evaluated. Vibrationally-resolved LIF spectra of benzene have been recorded. A metal containing free radical, CaCl has been trapped and observed using the apparatus.