How Large Are Low-Lying Molecular Rydberg States? Comparisons Between Experiment and Theory
✍ Scribed by A.M. Halpern
- Publisher
- Elsevier Science
- Year
- 1995
- Tongue
- English
- Weight
- 373 KB
- Volume
- 174
- Category
- Article
- ISSN
- 0022-2852
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✦ Synopsis
The "sizes" of low-lying molecular Rydberg states, estimated experimentally from the results of pressure perturbation spectroscopy, are compared with the results of ab initio molecular orbital calculations. Lennard-Jones 6-12 parameters associated with absorber-perturber pairs were assigned to the ground and excited states on the basis of pressure perturbation spectroscopy. These data are reported for the lowest Rydberg transitions of (\mathrm{NH}{3}), acetone, and (\mathbf{C H}{3} \mathbf{I}), as well as for the first two transitions of 1-azabicyclo[2.2.2 Joctane (ABCO). Increases in the sizes of these excited states relative to the respective ground states were compared with the results of (a b) initio calculations of the root-mean-square values of the electronic displacement, RMSR. Excited state calculations using configuration interaction (singles) with the (6-31+C^{*}) basis set (augmented in the case of (\mathrm{CH}{3} \mathrm{I}) ) were performed. Calculations are also reported for (\mathrm{CH}{2} \mathrm{O}, \mathrm{SO}{2}, \mathrm{CS}{2}), and 1,4-diazabicyclo[2.2.2 Joctane. Results show that increases in molecular size for intravalence transitions are nearly zero, while for the lower Rydberg transitions, (\triangle) (RMSR) values range between (0.23 \AA) (for (\mathrm{ABCO}) ) and (0.95 \AA) (for (\mathrm{NH}_{3}) ). The calculations on (\mathrm{ABCO}) and acetone indicate the involvement of (\mathrm{C}) atom (3 s) orbitals in the lowest excited (Rydberg) states. These findings are consistent with the experimental results obtained from pressure perturbation spectroscopy. 1995 Acadernic Press, Inc.