Faculty

Philip M. JohnsonPhilip M. Johnson, Research Professor and Professor Emeritus

B.S. University of Washington, 1962
Ph.D. Cornell University, 1967
Postdoctoral Fellow, University of Chicago, 1966-68
Visiting Fellow of the Joint Institute for Laboratory Astrophysics, 1976-77
Guggenheim Fellow, 1982-83
Fellow of the American Physical Society

561 Chemistry
Phone: (631) 632-7912
Email:

Physical Chemistry: Molecular Spectroscopy and Photophysics

The extremely high light levels available in pulsed lasers have created a rapid development in the understanding of the structure and dynamics of gas phase molecules and how they interact with the light. Our laboratory is actively involved in creating new techniques for the use of lasers in studying molecules and applying these techniques to prototype molecular systems. Many of the methods we have developed involve the ionization of the target molecules. In the high light flux from pulsed lasers the molecules keep absorbing the light until they lose an electron. The details of this electron loss, such as the wavelength dependence and the energy of the departing electron, give a great deal of information about both the bound and ionic states of the target molecule as well as indications about the photophysics of the various excited states. The gas phase systems we study range from small molecules such as nitric oxide and carbon dioxide to larger species including aromatics and molecular clusters. We have frequently discovered new excited electronic states of these systems, observed novel photochemical pathways, seen new physical phenomena, and refined our knowledge of the vibrational motions and geometric structures of excited states. In our analyses of the molecular spectra we are often guided by theoretical electronic structure calculations. Various techniques we have developed are in use in laboratories throughout the world in such practical applications as the determination of the details of combustion processes and the analysis of atmospheric gases. Recent developments in lasers and computers promise to enable even more powerful experiments to get at the details of molecular structure, photochemistry, and photophysics.

Recently we have been exploiting the properties of Rydberg molecules (where one electron is almost removed from the molecule and placed into a giant orbit) to develop new methods for obtaining the high resolution spectra of molecular cations. The exploitation of Rydberg molecules has enabled orders-of-magnitude increases in the resolution available for recording the spectra of molecular ions. A newly developed technique is called photoinduced Rydberg ionization spectroscopy (PIRI), providing high resolution access to the spectroscopy of the excited electronic states of ions. To accomplish this, we create a highRydberg state just below an ionic threshold and then excite the ion core. The spectrum of the resulting photoinduced autoionization is therefore basically that of the ion and has the resolution of the laser, while providing the information superior to a photoelectron spectrum.

Photoinduced Rydberg Ionization SpectroscopyPhotoinduced Rydberg Ionization Spectroscopy

Publications

Jason Hofstein, Haifeng Xu, Trevor Sears, and Philip Johnson, "The fate of excited states in jet-cooled aromatic molecules: Bifurcating pathways and very long-lived species from the S1 excitation of phenylacetylene and benzonitrile," J. Phys. Chem. A 112, 077367 (2008).

Haifeng Xu, Philip Johnson, and Trevor Sears, "Photoinduced Rydberg ionization spectroscopy of the B~ state of benzonitrile cation," J. Chem. Phys. 125, 164331 (2006).

Philip Johnson, Haifeng Xu, and Trevor Sears, "The calculation of vibrational intensities in forbidden electronic transitions," J. Chem. Phys. 125, 164330 (2006).

Haifeng Xu, Trevor Sears, and Philip Johnson, "Photoinduced Rydberg Ionization spectroscopy of Phenylacetylene: Vibrational assignments of the C~ state of the cation," J. Phys. Chem. A, 110, 7822-7825 (2006).

Andrew. B. Burrill, You K. Chung, Heather. A. Mann, and Philip M. Johnson, “The Jahn-Teller effect in the lower electronic states of benzene cation: Part III The ground state vibrations of C6H6+ and C6D6+,” J. Chem. Phys. 120, 8587-8599 (2004).

James Lightstone, Heather Mann, Ming Wu, Philip Johnson and Michael White, "Gas-phase production of molybdenum carbide, nitride, and sulfide clusters and nanocrystallites," J. Phys. Chem. B, 107, 10359-10366 (2003).

Andrew Burrill, Jia Zhou and Philip Johnson, “The Mass Analyzed Threshold Ionization Spectra of C6H6+ and C6D6+ obtained via the 3B1u Triplet State,” J. Phys. Chem. A, 107, 4601-4606 (2003).

H. K.Woo, K.-C Lau, J.-P Zhan, C. Y. Ng, Y.-S.Cheung, W. K. Li, and P. M. Johnson, "Vacuum Ultraviolet Laser Pulsed Field Ionization-Photoelectron Study of trans-Butene.", J. Chem. Phys.,119, 7789-7799 (2003).

Philip Johnson, "The Jahn-Teller effect in the lower electronic states of benzene cation: Part I. Calculation of linear parameters for the e2g modes." J. Chem. Phys., 117, 9991-10000 (2002).

The ionization potential and ground state cation vibrational structure of 1,4-dioxane, Burrill AB, Johnson PM CHEMICAL PHYSICS LETTERS 350 (5-6): 473-478 DEC 28 2001

MATI and PIRI investigations of torsional and Jahn-Teller interactions in cations. Johnson PM ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 221: 39-PHYS Part 2 APR 1 2001

Torsional analyses of trans-2-butene and propene cations: A comparative investigation of two prototypical ions with different degrees of symmetry, Burrill AB, Johnson PM JOURNAL OF CHEMICAL PHYSICS 115 (1): 133-138 JUL 1 2001

A modified Seya-Namioka monochromator with improved light intensity transfer, Maletta AM, Johnson PM REVIEW OF SCIENTIFIC INSTRUMENTS 71 (10): 3653-3656 OCT 2000

Reassessing the orbitals of pi systems using photoinduced Ryberg ionization spectroscopy Johnson PM, Anand R, Hofstein JD, LeClaire JE, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 108 (1-3): 177-187 JUL 2000

MATI and PIRI studies of the X~ and A~ state of trans-1,3-butadiene cation Hofstein JD, Johnson PM CHEMICAL PHYSICS LETTERS 316 (3-4): 229-237 JAN 14 2000

Assignment of the B+ state of the chlorobenzene cation using photoinduced Rydberg ionization (PIRI) spectroscopy Anand R, Hofstein JD, LeClaire JE, Johnson PM, Cossart-Magos C, JOURNAL OF PHYSICAL CHEMISTRY A 103 (45): 8927-8934 NOV 11 1999

Infrared spectrum of the CH2 out-of-plane fundamental of C2H5 , Sears TJ, Johnson PM, BeeBe-Wang J JOURNAL OF CHEMICAL PHYSICS 111 (20): 9213-9221 NOV 22 1999

Vibrational effects on the torsional motion of ethyl radical, Johnson PM, Sears TJ JOURNAL OF CHEMICAL PHYSICS 111 (20): 9222-9226 NOV 22 1999

Photoinduced Rydberg ionization (PIRI) spectroscopy of the B~ state of the fluorobenzene cation, Anand R, LeClaire JE, Johnson PM JOURNAL OF PHYSICAL CHEMISTRY A 103 (15): 2618-2623 APR 15 1999

A comparative investigation of Rydberg-state survival in several molecules using mass-analyzed threshold ionization, Hofstein JD, Goode JG, Johnson PM CHEMICAL PHYSICS LETTERS 301 (1-2): 121-130 FEB 19 1999

The observation of strong pseudo-Jahn-Teller activity in the benzene cation B~ 2E2g state, Goode JG, Hofstein JD, Johnson PM, JOURNAL OF CHEMICAL PHYSICS 107 (6): 1703-1716 AUG 8 1997

Photoinduced Rydberg ionization spectroscopy of phenol: The structure and assignment of the B~-state of the cation, LeClaire JE, Anand R, Johnson PM, JOURNAL OF CHEMICAL PHYSICS 106 (17): 6785-6794 MAY 1 1997

Probing the photoinduced Rydberg ionization process, Goode JG, LeClaire JE, Johnson PM INTERNATIONAL JOURNAL OF MASS SPECTROMETRY AND ION PROCESSES 159: 49-64 DEC 30 1996

Infrared laser transient absorption spectroscopy of the ethyl radical, Sears TJ, Johnson PM, Jin P, Oatis S JOURNAL OF CHEMICAL PHYSICS 104 (3): 781-792 JAN 15 1996

Photoinduced Rydberg ionization spectroscopy, Taylor DP, Goode JG, Leclaire JE, Johnson PM, JOURNAL OF CHEMICAL PHYSICS 103 (14): 6293-6295 OCT 8 1995

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