CHED 1370 |
| Assignment of vibrational spectroscopic data is complicated by the existence of anharmonicities and resonances. In order to assist in the analysis of spectra, these effects are calculated from ab initio computations of quartic potential energy surfaces (PES's). The purpose of this project is to compare the accuracies of the cc-pVTZ, hybrid, and aug-cc-pVQZ basis sets in PES computations for H2O, H2CO, HFCO, SCCl2, and their deuterated analogs. The computed PES's are assessed by comparing experimental and theoretical spectroscopic constants. The average absolute differences between theoretical and experimental harmonic frequencies ωi are 7.6 cm-1, 4.4 cm-1, and 4.5 cm-1 for the three basis sets (by increasing size). The average absolute differences for the anharmonicities xij are 2.6 cm-1, 2.5 cm-1, and 2.4 cm-1, respectively. The computed PES's are also assessed by comparing predicted and observed fundamental frequencies νi. The average absolute differences for the three basis sets are 10.6 cm-1, 6.6 cm-1, 6.5 cm-1. These results demonstrate that the anharmonic terms in the PES converge faster with basis set size than the harmonic terms. Thus it is found that calculations performed using the hybrid basis set, despite their lower computational cost, are comparable in accuracy to those performed using the larger basis set. |
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Undergraduate Research Poster Session: Physical Chemistry
2:00 PM-4:00 PM, Monday, March 26, 2007 Hyatt Regency Chicago -- Riverside Center, Poster
Division of Chemical Education |