J. Phys. Chem. 1992,96, 6875-6880 (32)Haser, M.; Almlof, J.; Scuseria, G.E. Chem. Phys. L e f f .1991, 181, 497. ( 7 3 ) Dunlan. 1.:. Brenner. D. W.: Mintmire. J. W.: Mowrev. R. C.: r , -B. -White, C. T. J . Phys. Chem. 1991, 95,'8737. (34)Ye, L.; Freeman, A. J.; Delley, B. Chem. Phys. 1992, 160, 415. (35)Kurita, N.; Kobayashi, K.; Kumahora, H.; Tago, K.; Ozawa, K. Chem. Phys. Letf. 1992, 188, 181. (36)(a) Dixon, D. A,; Andzelm, J.; Fitzgerald, G.;Wimmer, E. J . Phys. Chem. 1991, 95, 9197. (b) Christe, K. 0.;Curtis, E. C.; Mercier, H. P.; Sanders, J. C. P.; Schrobilgen, G.J.; Dixon, D. A. J . Am. Chem. SOC.1991, 113, 3351. (c) Christe, K. 0.; Wilson, R. D.; Wilson, W. W.; Bau, R.; Sukumar, S.;Dixon, D. A. J. Am. Chem. SOC.1991, 113, 3795. (d) Dixon, D. A.; Christe, K. 0. J . Phys. Chem. 1992, 96, 1018. (e) Arduengo, A. J., 111; Lattman, M.; Dixon, D. A.; Calabrese, J. C. Heteroatom 1991, 2, 395. (f) Dixon, D. A.; Arduengo, A. J., 111 Int. J . Quanfum Chem. Symp. 1991, 25, 269. (g) Sosa, C.; Andzelm, J.; Wimmer, E.; Dobbs, K. D.; Dixon, D. A. J . Phys. Chem., in press. (h) Dixon, D. A,; Gole, J. L. Chem. Phys. L e f f . 1992, 188, 560. (37)Hirschfelder, J. 0.; Curtiss, C. F.; Bird, R. B. Molecular Theory of Guses and Liquids; John Wiley and Sons: New York, 1964;p 950. (38)Cheng, L.-T.; Tam, W.; Stevenson, S.H.; Meredith, G.R.; Rikken, G.; Marder, S. R. J . Phys. Chem. 1991, 95, 11631. \--I
6875
(39)To compare this value to the experimental value by Wang and Cheng, the calculated value must be multiplied by 4/6 to account for the difference in the experimental and theoretical definitions of y. This gives y = 10.6 X esu. (40)Because y is isopropic, there is no need to recalculate the off-diagonal terms with the XFINE mesh. (41)This value is the average of the calculated r(C-C) and r(C=C). (42)The effect of geometry variations on y is small and together with previous semiempirical worklobsuggests that the effects of vibrational averaging on y should not be large. (43)(a) Hare, J. P.; Kroto, H. W.; Taylor, R. Chem. Phys. Len. 1991,177, 394. (b) Leach, S.;Vervloet, M.; DesprZs, A.; Brbheret, B.; Hare, J. P.; Dennis, T. J.; Kroto, H.W.; Taylor, R.; Walton, D. R. M. Chem. Phys. 1992, 160,451. (44)(a) Buchalter, B.; Meredith, G.R. Appl. Opt. 1982, 21, 3221. (b) Heflin, J. R.; Cai, Y.M.; Garito, A. F. J . Opt. SOC.Am. 1991, E8, 2132. (45)(a) Krusic, P. J.; Wasserman, E.; Parkinson, 8. A,; Malone, B.; Holler, E. R., Jr.; Keizer, P. N.; Morton, L. R.; Preston, K. F. J . Am. Chem. SOC.1991, 113, 6274. (b) Krusic, P. J.; Wasserman, E.; Keizer, P. N.; Morton, J. R.; Preston, K. F. Science 1991, 254, 1183. (c) Morton, J. R.; Preston, K. F.; Krusic, P. J.; Hill, S . A.; Wasserman, E. J . Am. Chem. SOC. 1992, 114, 5454.
Structured Effects of Rydberg-Rydberg Rotational Coupling on Intensities in the Zero Electron Kinetic Energy Threshold Photoionization Spectrum of State-Selected NO, Cregg P. Bryant, Yanan Jiang, Margarita Martin,+and Edward R. Grant* Department of Chemistry, Purdue University, West Lafayette, Indiana 47907 (Received: June 22, 1992)
Transitions from individual rovibrational levels of the 3pu 2Zu+ state, selected by double resonance, yield rotationally resolved threshold photoionization spectra of NO2. Observed photoionization cross sections conform with simple angular-momentum selection rules for transitions from a well-defined Hund's case b intermediate state to the case d Rydberg states that lie just below each successive threshold, except for the appearance of anomalous lines corresponding to large negative changes in ion-core rotational angular momentum. These latter transitions are found to be structured, and this structure is shown to reflect a Rydberg-Rydberg coupling hierarchy induced in zero field by the quadrupole moment of the finite core and facilitated in its final discrete-discrete step by low-field Stark mixing.
introduction Pulsed-field or zero electron kinetic energy (ZEKE) methods for the precise, state-detailed resolution of threshold photoionization processes have opened important new avenues of research in studies of electron-ejection dynamics, ion spectroscopy, and state-selected ion-molecule reaction~.I-~By the application of weak (
