The Journal of
Physical Chemistry
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0 Copyright 1995 by the American Chemical Society
VOLUME 99, NUMBER 6, FEBRUARY 9,1995
William A. Chupka
Photograph by Michael Marsland
Biographical Sketch Bill Chupka was born in 1923 in Pittston, Pennsylvania, and graduated from the University of Scranton in 1943. After serving three years in the U.S. Army, Chupka resumed his academic pursuits and earned M.S. and Ph.D. degrees from the University of Chicago under Joe Nayer in collaboration with Mark Inghram. His first academic position was as Instructor at Harvard College from 1951 to 1954, during which time he met and subsequently married Olive Pirani. Bill and Olive have two children, Jocelyn and Marc. He then moved to Argonne National Laboratory as an associate physicist in 1954, where he was to spend the next incredibly productive 20 years developing photoionization mass spectroscopy, largely in collaboration with Joe Berkowitz. He was a Guggenheim Fellow in 1961 and became a Senior Physicist at Argonne in 1962. Bill served as postdoctoral mentor to Patricia Dehmer starting in 1972, which initiated another long-lived collaboration spanning the next 20 years. He moved to Yale University in 1975 as Professor of Chemistry. At Yale, he worked closely with Steve Colson from 1980 to 1990 and is presently Emeritus Professor. JP9534444
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A Scientific Appreciation In 1964, Bill Chupka and his collaborator Joe Berkowitz focused a laser on a graphite surface and examined the species that were produced. In some ways the experiment represented the culmination of an extended program. Chupka had written his Ph.D. thesis (under the direction of Joe Mayer in collaboration with Mark Inghram) on the energetics of gaseous ions formed by vaporization of alkali halides. The mass spectrometric technique used was then adapted to the study of carbon vapor and the determination of the heat of vaporization of carbon. The experiments required an interrogation of the effusive flux from a high-temperature oven. It was an experimental setup that, with brief exceptions, Chupka was to use for much of the next 10 years. One such diversion was into an area in which Inghram had also played a pioneering role-the dissociative photoionization of polyatomic molecules. Bill realized that the diatomic molecule paradigm might not be appropriate and that a statistical model might instead be called for. He laid out clearly the roles that kinetic energy measurements, metastable intensities, and appearance potentials might play in any such judgment. Kinetic shifts are so much a part of our vocabulary today that an appearance potential 40 volts above a threshold energy seems quite unremarkable. A recurrent theme in Chupka’s analysis was the use of threshold laws for photoionization. A few years later he and Kaminsky used an analogous law for electron-induced ionization to obtain for the first time the sort of information that one now obtains routinely from a He I photoelectron spectrum. The entire analysis only makes sense if autoionization is negligible. Yet the results were to be vindicated when Chupka spent a year in Sweden using Lindholm’s charge exchange technique to get breakdown patterns for molecular ions. Some will call this luck; others will recognize judiciousness, a sense of knowing the limit beyond which an idea should not be pushed. Thus by the time of the laser-ablation experiment, Chupka had already taught us quite a lot. Some of his friends have wondered what would then have happened if the mass spectrometer in use at that time had been pushed to much higher masses. By way of an answer, let us look at some of the items that we would surely not understand so well today. The construction of a new apparatus, which centered around a 1 meter near-normal incidence monochromator, had opened up many possibilities. As often happens, it was f i s t turned to old purposes-the examination of high-temperature vapors and of photodissociative thresholds. Nevertheless, the intrusion of new ideas could not be thwarted. The continuity of oscillator strength at an ionization threshold was fist clearly demonstrated as was the role of rotational energy in facilitating the dissociation of C%+.
Perhaps the most important study to come from the photoionization mass spectrometer was the determination of the highresolution photoabsorption and photoionization spectra of cold para-H2. This study provided the first glimpse of rotational autoionization in molecules and showed that it would be possible to unravel the spectrum of the higher Rydberg states by using a para-Hz sample. The assignment of these states had been the quest of molecular spectroscopists for more than four decades; however, the spectrum had defied analysis owing to a combination of the effects of I-uncoupling, channel interaction, and the large rotational constant of H2, which resulted in electronic transitions with very widely spaced rotational lines. Even the liquid-nitrogen-temperaturespectrum of the ortho-para mixture 0022-3654/95/2099- 1620$09.OO/O
was too complicated to permit a rotational analysis of the higher Rydberg states. This fist photoionization spectrum of cold paraH2 helped pave the way for the complete understanding of the spectrum of molecular hydrogen. Up until this point autoionization had been something that, if one were fortunate, would not be important. Now it could be studied. Chupka and Berkowitz used the newly available resolution to demonstrate the vibrational propensity rule for autoionization, which had been proposed earlier by Berry. It was established via line-width measurements and then, in an experimental tour de force, by direct measurement of the photoelectron energies. An expected dependence of lifetime on principal quantum number was confirmed, and an unanticipated role for rotational autoionization was noted. Collisions are likewise something which a spectroscopist must always fight when pushing an apparatus to the limit. Again Chupka recognized the opportunity to turn a nuisance into an advantage. Perhaps most memorable was his application of the newly discovered propensity rules to create ions in well-defined vibrational levels. He then showed how endothermic ionmolecule reactions could be promoted by vibrational energy while exothermic reactions were, if anything, slightly retarded. State selection had come to ion-molecule chemistry. After viewing the exciting new data on rotational and vibrational autoionization in molecular hydrogen, Chupka quickly realized that the original photoionization mass spectrometer could not provide sufficient resolution to analyze the spectrum of molecular hydrogen to high principal quantum numbers. He immediately began the design and construction of a second-generation instrument that incorporated a 3 meter, near-normal incidence monochromator and a significantly improved helium continuum light source. That instrument, which was commissioned in the early 1970s, provided the definitive photoabsorption and photoionization spectra of paraH2, HD, and D2. The spectra clearly showed the effects of perturbations, vibrational and rotational autoionization, and predissociation to very high principal quantum numbers. For the past two decades, these spectra have served as tests for fundamental calculations of energy levels, line shapes, and competitive decay modes in molecular hydrogen. The new photoionization mass spectrometer was also used for a wide variety of studies of high-resolution photoionization spectra of small molecules such as N2, 02, CO, HF, HCl, HBr, HI, C02, and N20; for the study of state-selected ion-molecule reactions; and for the study of Rydberg state collisions and reactions. Papers from these extraordinarily productive years continued to be published throughout the 1970s and 1980s; indeed, the paper by Dehmer and Chupka that appears in this volume is based on data taken during the period 1972-1975. It was during this period that Chupka solidified his reputation as one of the dominant authorities on the properties and reactions of atomic and molecular Rydberg states. While Chupka’s expertise was widely appreciated in the vacuum ultraviolet community, the late 1970s brought forth an expanded role for photoionization with the development of multiphoton ionization (MPI), which exploited powerful, narrow band, and tunable dye lasers. MPI brought photoionization into the mainstream of chemical physics, as it provided a general tool for the state-selective detection of molecules and radicals with exquisite sensitivity. In many respects, lasers trivialized the acquisition of high-resolution spectra and data accumulated at a ferocious rate in the early 1980s. Chupka played a central 0 1995 American Chemical Society
Editorials role in the evolution of this fast-breaking field since he had already established the important paradigms in the context of interpreting spectra painstakingly collected over decades. Bill naturally assumed the role of mentor to younger (and occasionally older!) workers and was well known at conferences held during this time for his patient explanations of the proper way to look at something which the previous lecturer had just rediscovered. Chupka’s profound intuitive understanding and remarkably unassuming manner made him an ideal collaborator for others in the field. Teaming up with Steve Colson, Ed Eyler, and Mike White, the Yale-Brookhaven group quickly executed an important series of studies using double-resonance and photoelectron spectroscopies to exploit the advantages of laser multiphoton ionization. The most recent example where threshold ionization appears in a contemporary context involves the work of Schlag and Muller-Dethlefs, who developed the so-called zero electron kinetic energy or ZEKE spectroscopy using pulsed-field ioniza-
J. Phys. Chem., Vo2. 99,No. 6, 1995 1621 tion in the late 1980s. This technique yields very high resolution spectra of molecular and cluster ions by applying a weak electric field to selectively detect low-energy electrons which remain after the prompt electrons have drifted away from the ionization region. It was soon realized that the ZEKE mechanism involved field ionization of long-lived, high n, Rydberg states, and Chupka contributed explanations for some of the relevant properties of such states. Several of his papers in the early 1990s are really lectures on his way of thinking about Rydberg states to instruct us as much as break new scientific ground. We are grateful that he has continually taken the opportunity to teach us and share his enthusiasm for science. This volume acknowledges the profound impact he made on how we all have come to view molecular photoionization processes. C. E. Klots P. M. Dehmer M. A. Johnson JP953445W
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Scientific Collaborators Graduate Students. K. M. A. Refaey, S . T. Pratt, A. C. Puiu, W. Y. Cheung, P. J. Miller, H. Park, Y. Wang, R. J. Yokelson. Postdocs. M. W. Kaminsky, T. A. Walter, R. Spohr, P. M. Dehmer, J. L. Dehmer, L. Li, J. M. Smith. Research Collaborators. M. G. Inghram, R. F. Porter, H. E. Stanton, J. Berkowitz, G. B. Kistiakowsky, C. F. Giese, D. J. Meschi, H. A. Tasman, J. P. Schiffer, C. M. Stevens, C. Lifshitz, M. E. Russell, P. M. Guyon, D. Gutman, P. C. Killgoar, G. E. Leroi, D. Spence, W. T. Jivery, M. Matsuzawa, W. L. Luken, L. Andrews, S . D. Colson, M. Seaver, D. Gauyacq, M. G. White, P. Avouris, J. J. Wynne, A. M. Woodward, D. T. Biernacki, P. Chen, A. Sur, C. V. Ramana, J. B. Pallix, J. A. Berson, H. Lefebvre-Brion, E. E. Eyler, R. J. Lipert, J. H. Eland, R. J. Miller, M. J. DeLuca, D. M. Cyr, M. A. Johnson, E. deBeer, C. A. delange, A. L. Roche, K. B. Wiberg, C. M. Hadad, J. B.. Foresman. JP9534460
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Publications 1. Surface Ionization Source Using Multiple Filaments. M. G. Inghram and W. A. Chupka. Rev. Sci. Znstrum., 6A, 518-520 (1953). 2. Molecular Species Evaporating from a Carbon Surface. W. A. Chupka and M. G. Inghram. J. Chem. Phys., 21, 1313 (1953). 3. Investigation of the Heat of Vaporization of Carbon. W. A. Chupka and M. G. Inghram. J . Chem. Phys., 21, 371-372 (1953). 4. The Thermodynamics of Carbon Molecules as Detennined in the Mass Spectrometer. W. A. Chupka and M. G. Inghram. Proc. 6th Zntemational Symposium on Astrophysics, (1954) and Memoires de la Societe Royale des Sciences de Liege, 1 5 4 , 373-377 (1955). 5. Direct Determination of the Heat of Sublimation of Carbon. W. A. Chupka and M. G. Inghram. J. Chem. Phys., 22, 1472 (1954). 6. A Mass Spectrometric Study of Gaseous Species in the Si-Si02 System. R. F. Porter, W. A. Chupka and M. G. Inghram. J. Chem. Phys., 23, 216-217 (1955). 7. Water Dimer and Its Relation to Mass Spectrometric Measurement of C3 in Carbon Vapor. W. A. Chupka and M. G. Inghram. J . Chem. Phys., 23, 203-204 (1955). 8. Direct Determination of the Heat of Sublimation of Carbon with the Mass Spectrometer. W. A. Chupka and M. G. Inghram. J. Phys. Chem., 59, 100-104 (1955). 9. On the Dissociation Energies of SrO and MgO Molecules. R. F. Porter, W. A. Chupka and M. G. Inghram. J. Chem. Phys. 23, 1347 (1955). 10. A Mass Spectrometric Study on Barium Oxide Vapor. R. F. Porter, W. A. Chupka and M. G. Inghram. J. Chem. Phys., 23, 2159-2165 (1955). 11. Electron Multipliers in Mass Spectrometry: Effect of Molecular Structure. H. E. Stanton, W. A. Chupka and M. G. Inghram. Rev. Sci. Instrum., 27, 109 (1956). 12. The Dissociation Energy of Gaseous Lao. W. A. Chupka, M. G. Inghram and R. F. Porter. J . Chem. Phys., 24, 792-795 (1956). 13. Mass Spectrometric Study of the Kinetics of Nitrogen Afterglow. J. Berkowitz, W. A. Chupka and G. B. Kistiakowsky. J. Chem. Phys., 25, 457-466 (1956). 14. Mass Spectrometric Study of Gaseous Species in the B-B203 System. M. G. Inghram, R. F. Porter and W. A. Chupka. J. Chem. Phys., 25,498-501 (1956). 15. Polymeric Gaseous Species in the Sublimation of Molybdenum Trioxide. J. Berkowitz, M. G. Inghram and W. A. Chupka. J. Chem. Phys., 26, 842-845 (1957). 16. Thermodynamics of the Zr-ZrO2 System. The Dissociation Energies of ZrO and ZrOz. W. A. Chupka, J. Berkowitz and M. G. Inghram. J . Chem. Phys., 26, 1207- 1210 (1957). 17. Dissociation Energies from Thermodynamic Equilibria Studied with a Mass Spectrometer. M. G. Inghram, W. A. Chupka and J. Berkowitz. Memoires SOC.R. Liege, 13, 513-535 (1957). 18. Polymeric Gaseous Species in the Sublimation of Tungsten Trioxide. J. Berkowitz, W. A. Chupka and M. G. Inghram. J. Chem. Phys., 27, 85-86 (1957). 19. Thermodynamics of the V-0 System: Dissociation Energies of VO and V02. J. Berkowitz, W. A. Chupka and M. G. Inghram. J . Chem. Phys., 27,87-90 (1957). 0022-3654/95/2099-1623$09.00/0
20. Thermodynamics of the Ta-0 System: The Dissociation Energies of TaO and TaO;?. M. G. Inghram, W. A. Chupka and J. Berkowitz. J . Chem. Phys., 27, 569571 (1957). 21. Thermodynamics of the Ti-Ti203 System. J. Berkowitz, W. A. Chupka and M. G. Inghram. J. Phys. Chem., 61, 1569-1572 (1957). 22. Thermodynamic Studies of Some Gaseous Metallic Carbides. W. A. Chupka, J. Berkowitz, C. F. Giese and M. G. Inghram. J. Phys. Chem., 62, 611-614 (1958). 23. Effect of Unimolecular Decay Kinetics on the Interpretation of Appearance Potentials. W. A. Chupka. J . Chem. Phys., 30, 191-211 (1959). 24. Polymeric Gaseous Molecules in the Vaporization of Alkali Halides. J. Berkowitz and W. A. Chupka. J . Chem. Phys., 29, 653-657 (1958). 25. Dissociation Energies of Gaseous Alkali Halide Complex Ions and the Hydrated Ion K(H20)+. W. A. Chupka. J . Phys. Chem., 30, 458-465 (1959). 26. Mass Spectrometric Study of the Sublimation of Lithium Oxide. J. Berkowitz, W. A. Chupka, G. D. Blue and J. L. Margrave. J . Phys. Chem., 63, 644-648 (1959). 27. The Vaporization of Beryllium Oxide and Its Reaction with Tungsten. W. A. Chupka, J. Berkowitz and C. G. Giese. J . Chem. Phys., 30, 827-834 (1959). 28. Composition of Vapors in Equilibrium with Salts at High Temperatures. J. Berkowitz and W. A. Chupka. Ann. N.Y. Acad. Sci., 79, 1073-1078 (1960). 29. Kinetics of Unimolecular Decomposition of Excited Alkylamine Ions. W. A. Chupka and J. Berkowitz. J. Chem. Phys., 32, 1546-1553 (1960). 30. Heterogeneous Reactions Studied by Mass Spectrometry I. The Reaction of BzO3(s) with HzO(g). D. J. Meschi, W. A. Chupka and J. Berkowitz. J. Chem. Phys., 33, 530-533 (1960). 31. Heterogeneous Reactions Studied by Spectrometry 11. The Reaction of LizO(s) with HZO(g). J. Berkowitz, D. J. Meschi and W. A. Chupka. J . Chem. Phys., 33, 533540 (1960). 32. Energy Distribution and Fragmentation Processes Resulting from Electron Impact on Propane and n-Butane. W. A. Chupka and M. Kaminsky. J. Chem. Phys., 35, 1991-1998 (1961). 33. Double-Oven Experiments with Lithium Halide Vapors. J. Berkowitz, H. A. Tasman and W. A. Chupka. J. Chem. Phys., 36, 2170-2179 (1962). 34. Mass Spectrometric Studies of High-Temperature Systems. W. A. Chupka, J. Berkowitz, D. J. Meschi and H. A. Tasman. Advances in Mass Spectroscopy, R. M. Elliott, ed., 2, 99-109 (1963). 35. Thermodynamics and Kinetics of Vaporization Processes Studied by Mass Spectrometry. W. A. Chupka and J. Berkowitz. Appl. Spectros., 17(5), 130 (1963). 36. Vaporization Processes Involving Sulfur. J. Berkowitz and W. A. Chupka. J. Chem. Phys., 40, 287-295 (1964). 37. Dissociation of Butane Molecule Ions Formed in Charge Exchange Collisions with Positive Ions. W. A. Chupka and E. Lindholm. Arkiv Physik, 25, 349 (1963). 38. Mass Spectrometric Study of Vapor Ejected from Graphite and Other Solids by Focused Laser Beams. J. Berkowitz and W. A. Chupka. J. Chem. Phys., 40, 2735-2736 (1964). 0 1995 American Chemical Society
1624 J. Phys. Chem., Vol. 99, No. 6, 1995 39. Energy Dependence of Cross Sections for CollisionInduced Dissociation and Endothermic Ion-Molecule Reactions. K. M. Refaey and W. A. Chupka. J. Chem. Phys., 43, 2544-2545 (1965). 40. Experimental Search for Stable, Fractionally Charged Particles. W. A. Chupka, J. P. Schiffer and C. M. Stevens. Phys. Rev. Lett., 17, 60-65 (1966). 41. Photoionization of High-Temperature Vapors. I. The Iodides of Sodium, Magnesium, and Thallium. J. Berkowitz and W. A. Chupka. J. Chem. Phys., 45, 1287-1298 (1966). 42. Equilibrium Composition of Selenium Vapor; The Thermodynamics of the Vaporization of HgSe, CdSe, and SrSe. J. Berkowitz and W. A. Chupka. J . Chem. Phys., 45,4289-4302 (1966). 43. Photoionization of Ethane, Propane, and nButane with Mass Analysis. W. A. Chupka and J. Berkowitz. J. Chem. Phys., 47, 2921-2933 (1967). 44. Photoionization of the CF3 Free Radical. C. Lifshitz and W. A. Chupka. J . Chem. Phys., 47,3439-3443, (1967). 45. Reactions of Ions Produced in Selected States by Photoionization. W. A. Chupka. Fifteenth Annual Conference on Mass Spectrometry and Allied Topics, ASTM Committee, E-14, Denver, Colorado, 63 (1967). 46. Vibrations and Thermodynamic Properties of Hexasulfur. J. Berkowitz, W. A. Chupka, E. Bromels and R. Linn Belford. J . Chem. Phys., 47, 4320-4324 (1967). 47. High-Resolution Photoionization and Mass Analysis of Small Molecules. J. Berkowitz and W. A. Chupka. Fifh International Con$ on the Physics of Electronic and Atomic Collisions, Abstracts of Papers, Leningrad, I. P. Flaks and E. S. Solovyov, eds., 608-610 (1967). 48. Comment on the Composition of Selenium Vapor. J. Berkowitz and W. A. Chupka. J. Chem. Phys., 48, 5743-5744 (1968). 49. Mass-Spectrometric Study of the Photoionization of Methane. W. A. Chupka. J. Chem. Phys., 48, 23372341 (1968). 50. Photoionization of the Hz Molecule Near Threshold. W. A. Chupka and J. Berkowitz. J. Chem. Phys., 48,57265728 (1968). 51. Photoionization of CH3; Heat of Formation of CHz. W. A. Chupka and C. Lifshitz. J. Chem. Phys., 48,11091115 (1968). 52. Ion-Molecule Reactions of NH3+ by Photoionization. W. A. Chupka and M. E. Russell. J . Chem. Phys., 48, 1527-1533 (1968). 53. Ion-Molecule and Chemi-Ionization Reactions in HZ by Photoionization. W. A. Chupka, M. E. Russell and K. Refaey. J. Chem. Phys., 48, 1518-1527 (1968). 54. Photoionization of the Lower Aliphatic Alcohols with Mass Analysis. Kame1 M. A. Rafaey and W. A. Chupka. J. Chem. Phys., 48(11), 5205-5219 (1968). 55. Photoionization of HCN: The Electron Affinity and Heat of Formation of CN. J. Berkowitz, W. A. Chupka and T. A. Walter. J . Chem. Phys., 50, 1497-1500 (1969). 56. Photoionization of Ethylene with Mass Analysis. W. A. Chupka, J. Berkowitz and K. M. A. Refaey. J . Chem. Phys., 50, 1938-1941 (1969). 57. Photoionization Study of Ion-Molecule Reactions in Mixtures of Hydrogen and Rare Gases. W. A. Chupka and Morley E. Russell. J. Chem. Phys., 49,5426-5437 (1968).
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58. Photoionization of High-Temperature Vapors. VI. SZ, Sez, and Te2. J. Berkowitz and W. A. Chupka. J. Chem. Phys., 50, 4245-4250 (1969). 59. Mass Spectrometric Study of the Photoionization of c2F4 and CF4. T. A. Walters, C. Lifschitz, W. A. Chupka and J. Berkowitz. J . Phys. Chem., 51, 3531 (1969). 60. Photoelectron Spectroscopy of Autoionization Peaks. J. Berkowitz and W. A. Chupka. J. Chem. Phys., 51,2341 (1969). 61. High Resolution Photoionization Study of the H2 Molecule. W. A. Chupka and J. Berkowitz. J. Chem. Phys., 51, 4244 (1969). 62. Diatomic Ions of Noble Gas Fluorides. J. Berkowitz and W. A. Chupka. Chern. Phys. Lett., 7, 447 (1970). 63. Photoionization Studies of Fz, HF, DF, and the Xenon Fluorides. J. Berkowitz, W. A. Chupka, P. M. Guyon, M. Holloway and R. Spohr. Advances in Mass Spectrometry, A. Quale, ed., 5, 112 (1971). 64. Photoionization Mass Spectrometric Study of XeFZ, XeF4 and XeF6. J. Berkowitz, W. A. Chupka, P. M. Guyon, J. H. Holloway and R. Spohr. J . Phys. Chem.,75,1461 (1971). 65. Ion-Molecule Reactions in Ethanol by Photoionization. M. E. Russell and W. A. Chupka. J . Phys. Chem., 75,3797 (1971). 66. Effect of Thermal Energy on Ionization Efficiency Curves of Fragment Ions. W. A. Chupka. J . Chem. Phys., 54, 1936 (1971). 67. Photoionization of Methane: Ionization Potential and Proton Affinity of C h . W. A. Chupka and J. Berkowitz. J . Phys. Chem., 54, 4256 (1971). 68. Kinetic Energy of Ions Produced by Photoionization of HF and F2. W. A. Chupka and J. Berkowitz. J. Chem. Phys., 54, 5126 (1971). 69. Photoionization Mass Spectrometric Study of Fz, HF and DF. J. Berkowitz, W. A. Chupka, P. M. Guyon, J. H. Holloway and R. Spohr. J . Chem. Phys., 54, 5165 (1971). 70. Electron Affinities of Halogen Diatomic Molecules as Determined by Endoergic Charge Transfer. W. A. Chupka, J. Berkowitz and D. Gutman. J . Phys. Chem., 55, 2724 (1971). 71. Electron Affinities of Oz,O3, NO, NO2, NO3 by Endoergic Charge Transfers. J. Berkowitz, W. A. Chupka and D. Gutman. J . Chem. Phys., 55, 2733 (1971). 72. Threshold Photoelectron Detection for Use in the Vacuum Ultraviolet. R. Spohr, P. M. Guyon, W. A. Chupka and J. Berkowitz. Rev. Sci. Instrum., 42, 1872 (1971). 73. Photoionization of HOF with Mass Anaysis. J. Berkowitz, E. H. Appelman and W. A. Chupka. J . Chem. Phys., 58, 1950 (1973). 74. Photoionization Mass Spectrometric Study of NO. A Closer Look at the Threshold Region. P. C. Killgoar, G. E. Leroi, J. Berkowitz and W. A. Chupka. J. Chem. Phys., 58, 803 (1973). 75. Ion-Molecule Reactions by Photoionization Techniques. W. A. Chupka. Ion Molecule Reactions, J. L. Franklin, ed., 1, 33 (1972). 76. Photoionization Mass Spectrometry of F20. J. Berkowitz, P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 59, 925 (1973). 77. Photoionization Study of NOz. I. The Ionization Potential. P. C. Killgoar, Jr., G. E. Leroi, W. A. Chupka and J. Berkowitz. J . Chem. Phys., 19, 1370 (1973).
Editorials 78. Photoionization of Atomic Oxygen from 920 to 650 A. P. M. Dehmer, J. Berkowitz and W. A. Chupka. J. Chem. Phys., 59, 5777 (1973). 79. Photoionization of Atomic Nitrogen. P. M. Dehmer, J. Berkowitz and W. A. Chupka. J. Chem. Phys., 60,2676 (1974). 80. Measurement of Resonances in Atomic Oxygen by Electron Transmission Spectroscopy. D. Spence and W. A. Chupka. Phys. Rev., A10, 71 (1974). 8 1. Photoionization and Fragmentation of Polyatomic Molecules. W. A. Chupka. Chemical Spectroscopy and Photochemistry in the Vacuum-Ultraviolet, C. Sandorfy, P. J. Ausloos and M. B. Robin, eds., 433-464 (1974). 82. Nonstatistical Emission from Metastable Autoionizing States of 0 I. P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 62, 584 (1975). 83. Photoionization Study of the Reaction of Oz+(a411)with 0 2 . P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 62, 2228 (1975). 84. High Resolution Study of Photoionization Processes in 0 2 . P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 62, 4525 (1975). 85. Effects of Internal Energy on Ion-Molecule Reactions. W. A. Chupka. Interactions Between Ions and Molecules, Pierre Ausloos, ed., 249-263 (1975). 86. High Resolution Photoionization Study of Ion-Pair Formation in H2, HD and D2. W. A. Chupka, P. M. Dehmer and W. T. Jivery. J . Chem. Phys., 63, 3929 (1975). 87. Wavelength Dependence of the Photoelectron Angular Distributions of the Rare Gases. J. L. Dehmer, W. A. Chupka, J. Berkowitz and W. T. Jivery. Phys. Rev., A12, 1966, (1975). 88. Photoionization Mass Spectrometric Study of Formaldehyde HzCO, HDCO and DzCO. P. M. Guyon, W. A. Chupka and J. Berkowitz. J . Chem. Phys., 64, 1419 (1976). 89. Threshold Photoelectron Spectra of HF, DF and F2. P. M. Guyon, R. Spohr, W. A. Chupka and J. Berkowitz. J. Chem. Phys., 65, 1650 (1976). 90. Search for Fractionally Charged Particles in Lunar Soil. C. M. Stevens, J. P. Schiffer and W. A. Chupka. Phys. Rev., D14, 716 (1976). 91. Very High Resolution Study of Photoabsorption, Photoionization and Predissociation in H2. P. M. Dehmer and W. A. Chupka. J . Chem. Phys., 65, 2243 (1976). 92. On the Mechanism for Vibrational Autoionization in Hz*. P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 66, 1972 (1977). 93. Rotational Effect in the Ionization of a Highly Excited Atom by Collision with a Polar Molecule. M. Matsuzawa and W. A. Chupka. Chem. Phys. Lett., 50,373 (1977). 94. Competition Between Autoionization and Radiative Emission in the Decay of Excited States of the Oxygen Atom. P. M. Dehmer, W. L. Luken and W. A. Chupka. J. Chem. Phys., 67, 195 (1977). 95. Vibrational Effects in Coulomb-Explosion Experiments. S . T. Pratt and W. A. Chupka. J . Chem. Phys., 52,443 (1980). 96. Predissociation of the 3pn D1&+ state in Hz, HD and Dz. P. M. Dehmer and W. A. Chupka. Chem. Phys. Lett., 70, 127 (1980).
J. Phys. Chem., Vol. 99, No. 6, 1995 1625 97. Effects of Vibronic Interaction and Autoionization on the Photoelectron Spectrum of N20. P. M. Dehmer, J. L. Dehmer and W. A. Chupka. J. Chem. Phys., 73, 126 (1980). 98. Photoionization Study of the Kinetics of Unimolecular Decomposition of Halobenzene Ions. S . T. Pratt and W. A. Chupka. J . Chem. Phys., 62, 153 (1981). 99. Mass Spectrometric Observation of the Stable Negative Molecular Ions HI- and HzI-. David Spence, W. A. Chupka and C. M. Stevens. J. Chem. Phys., 76, 2759 (1982). 100. Search for Long-Lived Doubly-ChargedAtomic Negative Ions. D. Spence, W. A. Chupka and C. M. Stevens. Phys. Rev., 26, 654 (1982). 101. Vibronic Absorption Spectra of the Biphenyl and Biphenyl-dlo Cations in Solid Argon. A. C. Puiu, L. Andrews, W. A. Chupka and S . D. Colson. J . Chem. Phys., 76, 3854 (1982). 102. Optical-Optical Double Resonance Multiphoton Ionization Spectroscopy of NO. M. Seaver, W. Y. Cheung, D. Gauyacq, W. A. Chupka and S . D. Colson. Laser Techniques for Extreme Ultraviolet Spectroscopy, T. J. McIlrath and R. R. Freeman, eds., (1982). 103. Observation of Rydberg (C21T)-Valence(B211) Interactions in NO by Multiphoton Photoelectron Spectroscopy. M. G. White, M. Seaver, W. A. Chupka and S . D. Colson. Phys. Rev. Lett., 49, 28 (1982). 104. Rydberg-Rydberg Transitions of NO Using an OpticalOptical Double Resonance Multiphoton Ionization Technique. W. Y. Cheung, W. A. Chupka, S . D. Colson, D. Gauyacq, P. Avouris and J. J. Wynne. J. Chem. Phys., 78, 3625 (1983). 105. Photodissociation Spectrum of CH3I+ Prepared by Multiphoton Ionization. W. A. Chupka, S. D. Colson, M. S . Seaver and A. M. Woodward. Chem. Phys. Lett., 95, 171 (1983). 106. Double Resonance Multiphoton Ionization Studies of High Rydberg States in NO. M. Seaver, W. A. Chupka, S . D. Colson and D. Gauyacq. J. Phys. Chem., 87, 2226 (1983). 107. Two Color Laser Studies of the Multiphoton Ionization and Dissociation of Trans 1,3-Butadiene. A. M. Woodward, W. A. Chupka, S . D. Colson. J. Phys. Chem., 88, 4567 (1984). 108. Photoabsorption and Photoionization of HD. P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 79, 1569 (1983). 109. Four-Photon Resonant Ionization of NO via the A2Z+ State: Photoelectron Spectra and Angular Distribution. M. G. White, W. A. Chupka, M. Seaver, A. M. Woodward and S . D. Colson. J. Chem. Phys., 80, 678 (1984). 110. Photoionization of N2XZ+g, v” = 0 and 1 Near Threshold-Preionization of the Worley-Jenkins Rydberg Series. P. M. Dehmer, P. J. Miller and w. A Chupka. J . Chem. Phys., 80, 1030 (1984). 111. Electron Photodetachment from Transient Negative Ions in the Multiphoton Ionization of CH3I. W. A. Chupka, A. M. Woodward and S. D. Colson. J. Chem. Phys., 82, 4880 (1985). 112. Autoionization of the 4f Rydberg State of the NO Molecule. E. E. Eyler, W. A. Chupka, S. D. Colson and D. T. Biemacki. Chem. Phys. Lett., 119, 177 (1985).
1626 J. Phys. Chem., Vol. 99, No. 6, 1995 113. High Resolution One-Photon Ionization Spectrum of NO Using Third-Harmonic Generation. P. J. Miller, P. Chen and W. A. Chupka. J. Chem. Phys., 120, 217 (1985). 114. Multiphoton Spectroscopy and Analysis of the E211+X211 Band of CH. P. Chen. W. A. Chupka and S . D. Colson. Chem. Phys. Lett., 121, 405 (1985). 115. Vibrational Analysis of the A-X Photodissociation Spectrum of CH3I+. A. M. Woodward, S . D. Colson, W. A. Chupka and M. G. White. J . Phys. Chem., 90,274 (1986). 116. Probing Excited States of NO Involved in Multistate Interactions Using the OODR-MPI Technique. W. Y. Cheung, W. A. Chupka, S . D. Colson, D. Gauyacq, P. Avouris and J. J. Wynne. J . Phys. Chem., 90, 1086 (1986). 117. Rydberg Valence Interactions in the IIg States of 0 2 . A Sur,C. V. Ramana, W. A. Chupka and S . D. Colson. J. Chem. Phys., 84, 69 (1986). 118. High Power Laser Photochemistry: Production of Neutral Atomic and Small Molecular Fragments by W Multiphoton Dissociation. P. Chen., J. B. Pallix, W. A. Chupka and S . D. Colson. J. Chem. Phys., 84, 5208 (1986). 119. Photoelectron Spectroscopy of the Excited States of the CH Radical. J. B. Pallix, P. Chen, W. A. Chupka and S . D. Colson. J . Chem. Phys., 84, 5208 (1986). 120. Flash Pyrolytic Production of Rotationally Cold Free Radicals in a Supersonic Jet. Resonant Multiphoton Spectrum of the 3p 2A2('CX2A2)' Origin Band of CH3. P. Chen, S . D. Colson, W. A. Chupka and J. A. Berson. J . Phys. Chem., 90, 2319 (1986). 121. Vibrational Effects in the Spin-Orbit Autoionization of HBr. H. Lefebvre-Brion, P. M. Dehmer and W. A. Chupka. J. Chem. Phys., 85, 45 (1986). 122. Resonant Multiphoton Ionization Spectrum and Electronic Spectrum of CH Radical. New States and Assignments Above 50,000 cm-'. P. Chen, J. B. Pallix, W. A. Chupka and S . D. Colson. J. Chem. Phys., 86, 516 (1987). 123. Photoionization of Molecular Rydberg States; H2 C I l l u and Its Doubly Excited States. W. A. Chupka. J. Chem. Phys., 87, 1488 (1987). 124. Predissociation-Induced Rovibrational Autoionization and Zero-Energy Electrons. W. A. Chupka, P. J. Miller and E. E. Eyler. J . Chem. Phys., 88, 3032 (1988). 125. Dynamics and Spectroscopic Manifestations of TwoPhoton Bound-Bound Absorption Through a Repulsive Intermediate State. L. Li, R. J. Lipert, H. Park, W. A. Chupka and S . D. Colson. J . Chem. Phys., 87, 6767 (1987). 126. Spin-Orbit and Electronic Autoionization in HC1. H. Lefebvre, P. M. Dehmer and W. A. Chupka. J . Chem. Phys., 88, 811 (1988). 127. Spectroscopy and Photophysics of I l l g and 311g RydbergIon-Pair States of C12 Revealed by Multiphoton Ionization. L. Li, R. J. Lipert, H. Park, W. A. Chupka and S. D. Colson. J . Chem. Phys., 88, 4608 (1988). 128. Observation of Strong Rydberg-Valence Mixing in the E 311,-State of 0 2 by 3 f l MPI Photoelectron Spectroscopy. P. J. Miller, L. Li, W. A. Chupka and S . D. Colson. J . Chem. Phys., 88, 2972 (1988). 129. Vibrationally Autoionizing Rydberg States of "3. P. J. Miller, W. A. Chupka and J. H. Eland. Chem. Phys., 122, 2972 (1988).
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130. Observation of the vlfmv2 Combination Band in the 'AI Rydberg State of "3. P. J. Miller, S . D. Colson and W. A. Chupka. Chem. Phys. Lett., 145,183 (1988). 131. Rydberg Photochemistry of Methyl Radicals. P. Chen, S . D. Colson and W. A. Chupka. Chem. Phys. Lett., 147, 466, (1988). 132. Shape-Resonance and Non-Franck-Condon Behavior in the Photoelectron Spectra of 0 2 Produced by 2 f l MPI via 3sa Rydberg States. P. J. Miller, L. Li, W. A. Chupka and S . D. Colson. J. Chem. Phys., 89, 3921 (1988). 133. Autoionization Dynamics in the Valence-Shell Photoionization Spectrum of CO. J. E. Hardis, T. A. Ferret, S . H. Southworth, A. C. Parr, P. Roy, J. L. Dehmer, P. M. Dehmer and W. A. Chupka. J . Chem. Phys., 89, 812 (1988). 134. Production of Vibrationally State-Selected 0 2 + via Newly Discovered 3s-3d and 5s-4d Rydberg States of 02. H. Park, P. J. Miller, W. A. Chupka and S . D. Colson. J. Chem. Phys., 89, 3919 (1988). 135. Shape Resonance Influence on the Photoelectron Angular Distribution from 0 2 C 311gv=O-3. P. J. Miller, W. A. Chupka, J. Winniczek and M. G. White. J . Chem. Phys., 89, 4058 (1988). 136. Adiabatic Dissociation of Photo-Excited Chlorine Molecules. L. Li, R. J. Lipert, J. LoBue, W. A. Chupka and S . D. Colson. Chem. Phys. Lett., 151, 335 (1988). 137. Multiphoton Optical and Photoelectron Spectroscopy of the 4s-3d and 5s-4d Rydberg Complexes of 0 2 . H. Park, P. J. Miller, W. A. Chupka and S . D. Colson. J . Chem. Phys., 89, 6676 (1988). 138. Anomalous Line Shapes in Delayed Optical-Optical Double Resonance Studies of N2. L. Li, W. A. Chupka and S . T. Pratt. J. Chem. Phys., 90, 606 (1989). 139. Multiphoton Ionization Studies of NO: Spontaneous Decay Channels in the 4pn K *II(v=2) Rydberg State. R. J. Miller, L. Li, Y. Wang, W. A. Chupka and S . D. Colson. J . Chem. Phys., 90, 754 (1989). 140. Observation and Analysis of the 3d.7~IXg+Rydberg State of 0 2 by (2+1) Multiphoton Ionization. H. Park, L. Li and W. A. Chupka. Chem. Phys. Lett., 162,317 (1989). 141. Identification of the 3d.z 'Ag Rydberg State of 0 2 by Multiphoton Ionization and Polarization Studies. H. Park, L. Li and W. A. Chupka. J . Chem. Phys., 92,61 (1990). 142. Two-Photon Spectroscopy of the 3d Rydberg States of 02: and 3@g States. H. Park, L. Li, W. A. Chupka and H. Lefebvre-Brion. J. Chem. Phys., 92, 5835 (1990). 143. Isotopic Fractionation in Low Temperature Ion-Molecule Exchange Reactions: Enrichment of 22N,+ Clusters Formed by Association in an Ionized Free Jet. M. J. DeLuca, D. M. Cyr, W. A. Chupka and M. A. Johnson. J . Chem. Phys., 92, 7349 (1990). 144. Identification of the nd A and X States and the 193@+X3&Transition of 0 2 by Resonant Multiphoton Ionization. R. J. Yokelson, R. J. Lipert and W. A. Chupka. J . Chem. Phys., 97, 6144 (1992). 145. (2+1) REMPI-PES of the OH Radical. E. deBeer, C. A. delange, Y. Wang and W. A. Chupka. J. Chem. Phys., 94, 7634 (1991). 146. s and d Rydberg Complexes of NO Probed by Double Resonance Multiphoton Ionization in the Region n* = 5 to n* = 25; Multichannel Defect Analysis 11. D. Gauyacq, A. L. Roche, M. Seaver, S . D. Colson and W. A. Chupka. Mol. Phys., 71, 1311 (1990).
Editorials 147. Rotationally Resolved Photofragmentation Spectroscopy of CH+ Formed by Resonance-Enhanced Multiphoton Ionization. Y. Wang, L. Li and W. A. Chupka. Chem. Phys. Lett., 185, 478 (1991). 148. (2+ 1) Resonance-Enhanced Multiphoton Ionization Studies of the CH D2rI (v=2) State. Y . Wang, L. Li and W. A. Chupka. Chem. Phys. Lett., 192, 348 (1992). 149. Identification of the ndA and Z States and the 1,3@-X3$Transition of 0 2 by Resonant Multiphoton Ionization. R. J. Yokelson, R. J. Lipert and W. A. Chupka. J. Chem. Phys., 97, 6144 (1992). 150. Identification of the nsu and nd II Rydberg States of 02 for n=3-5. R. J. Yokelson, R. J. Lipert and W. A. Chupka. J. Phys. Chem., 97, 6153 (1992). 151. Prescription for Preparation of Molecular Ions in Selected Rotational States. Y. Wang and W. A. Chupka. Chem. Phys. Lett., 200, 192 (1992). 152. Electronically Excited States of Ethylene. K. B. Wiberg,
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C. M. Hadad, J. B. Foresman and W. A. Chupka. J. Phys. Chem., 96, 10756 (1992). Factors Affecting Lifetimes and Resolution of Rydberg States Observed in Zero-Electron-KineticEnergy Spectroscopy. W. A. Chupka. J. Chem. Phys., 98, 4520 (1993). Lifetimes of Very High Rydberg States of Aromatic Molecules. W. A. Chupka. J. Chem. Phys., 99, 5800 (1993). Reactions of Rydberg States of Molecular Hydrogen. S. T. Pratt, J. L. Dehmer, P. M. Dehmer, and W. A. Chupka. J . Chem. Phys., 101, 882 (1994). Rydberg State Reactions of Atomic and Molecular Hydrogen. P. M. Dehmer and W. A. Chupka. J. Phys. Chem. (1994). Electron Transfer in High-n Rydberg States. J. M. Smith and W. A. Chupka. J . Chem. Phys. (in press). JP953447G
