Peter B. Kelly

Professor

Email: kelly@chem.ucdavis.edu

Physical Chemistry

A.B., Dartmouth College, 1976. Ph.D., Pennsylvania State University, 1981. Research Associate, Princeton university, 1981-83. Research Associate, University of Oregon, 1983-86. Appointed to faculty, UC Davis, 1986-.

Research Interests

My research efforts are concentrated in three areas: the use of mass spectrometry in environmental chemistry, the application of laser spectroscopy to the study of combustion processes, and the investigation of fundamental properties of hydrocarbon radicals.

Environmental analytical work in my laboratory involves development of new analytical techniques using laser desorption mass spectrometry and its application to examine airborne particles collected on sampling filters. Laser desorption - laser photoionization time of flight mass spectrometry (LDLPMS) is aptly suited to environmental analyses. The laser desorption and ionization process is not impeded by salts and gives essentially instantaneous volatilization of the sample. Thus the LDI-TOF mass spectrometer is an effective means to directly analyze soot or fly ash samples for polycyclic aromatic hydrocarbons and their chlorinated analogs, eliminating labor intensive and costly extraction procedures. Our method provides rapid analysis of the samples without any wet chemistry. It also can be adapted for use with a field portable system.

The analysis of organics with LDI-TOF has involved polycyclic aromatic hydrocarbon compounds (PAH) and their derivatives [Analytical Chemistry, Vol. 68, p. 2319, 1996] and [Journal of the American Society for Mass Spectrometry, Vol. 8, p. 630. 1997].

Our work on arsenic oxides [Analytical Chemistry, Vol. 68, p 4052, 1996] was the first use of time of flight mass spectrometry for metal oxide speciation. The determination of oxidation state in arsenic oxides is of concern due to the carcinogenic activity of arsenic (III) oxide. We are able to determine the relative amounts of arsenic (III) oxide and arsenic (V) oxide in a sample by examination of the cluster ions produced in the laser desorption ionization process. We are currently concluding a similar study for the speciation of Cr (III), Cr (IV), and Cr (VI). Future studies will examine antimony, selenium, and iron oxides.

We have worked in collaboration with the engineering groups on campus to examine combustion processes in model incinerators. We have used a variety of techniques including LDI-TOF mass spectrometry and laser spectroscopy. We have conducted an examination of combustion generated aerosols from trichloroethylene flames and arsenic containing flames [Combustion and Flame, Vol. 98, p. 259, 1994], [Environmental Health Perspectives, Vol. 104, p. 734, 1996].

We are using resonance Raman laser spectroscopy in the investigation of fundamental properties of hydrocarbon radicals. The goal of our experiments is to examine the properties of molecular electronic states; that is: excited state potential functions, photodissociation pathways, and ground state geometry and anharmonicity.

Resonance Raman Spectroscopy has been used to examine the methyl, ethyl, allyl, 1-methylallyl, 2-methylallyl, and 2-chloroallyl radicals [Journal of Physical Chemistry, Vol. 100, p. 7743, 1996], [Journal of Physical Chemistry, Vol. 100, p. 7772, 1996]. Free radicals are a class of molecules that are both most interesting and most elusive. These species are of interest because of their central role in combustion kinetics, polymerization reactions, molecular astrophysics, and theoretical chemistry. However, these species are among the most reactive species known and thus the most difficult to study. Small gas phase organic free radicals are produced by laser photolysis and probed by time resolved resonance Raman spectroscopy. The observed frequencies yield the ground state vibrational structure of the radical. Analysis of the intensity pattern can give the excited state vibrational structure and excited state dynamics. The variation of the signal intensity with delay time provides the rate of reaction for the radical with a buffer gas of interest. The impact of this work varies from engineering studies of flame diagnostics to the examination of fundamental chemical structure and bonding. Future work on this project involves the examination of methylene radical and extension of the resonance Raman method into the vacuum ultraviolet region of the spectrum to examine higher lying electronic states.

Publications

Kennedy, I.M., Y. Zhang, A.D. Jones, C.P.Y. Chang, and P.B. Kelly. 1999. The morphology of chromium emissions from a laminar hydrogen diffusion flame. Combustion and Flame, 116, 233-242.

Bezabeh, D.Z., A.D. Jones, L.L. Ashbaugh, and P.B. Kelly. Screening of aerosol filter samples for PAHs and nitro-PAHs by laser desorption ionization TOF mass spectrometry. Aerosol Science and Technology, in press.

Zhang, Y., Y. Yoon, P.B. Kelly, and I.M. Kennedy. 1998. Measurement of quenching cross sections for laser induced fluorescence of atomic arsenic. Applied Optics, 37, 7132-36.

Bezabeh, D.Z., T.M. Allen, E.M. McCauley, P.B. Kelly, and A.D. Jones. 1997. Negative ion laser desorption ionization time of flight mass spectrometry of nitrated polycyclic aromatic hydrocarbons. J. Amer. Soc. Mass Spec., 8, 630-635.

Johnson, B.R., C. Kittrell, P.B. Kelly, and J.L. Kinsey. 1996. Resonance raman spectroscopy of dissociative polyatomic molecules. J. Phys. Chem., 100, 7743-7764.

Allen, T.M., D.Z. Bezabeh, C.H. Smith, E.M. McCauley, A.D. Jones, D.P.Y. Chang, I.M. Kennedy, and P.B. Kelly. 1996. Speciation of arsenic oxides using laser desorption/ionization time-of-flight mass spectrometry. Anal. Chem., 68, 402-405.

Tarrant, D.H., J.D. Getty, X. Liu, and P.B. Kelly. 1996. Resonance raman spectroscopy of the 1-methylallyl radical. J. Phys. Chem., 100, 7772-7777.

Dotter, R.N., C.H. Smith, M.K. Young, P.B. Kelly, A.D. Jones, E.M. McCauley, and D.P.Y. Chang. 1996. Laser desorption/ionization time-of-flight mass spectrometry of nitrated polycyclic aromatic hydrocarbons. Anal. Chem., 68, 2319-2324.

Getty, J.D., X. Liu, and P.B. Kelly. 1996. Observation of the 2-methylallyl radical by resonance raman spectroscopy. J. Chem. Phys., 104, 3176-3180.