Glenn Stark

Department of Physics
Wellesley College
Wellesley, MA
 
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Research and Professional Information

Education:

Massachusetts Institute of Technology, B.S., Physics (1976)
University of California, Berkeley, Ph.D., Physics (1985)

Research Interests:

My research is in the field of experimental molecular spectroscopy. My laboratory programs emphasize, but are not limited to, molecular transitions of interest to the astrophysical, aeronomic, and planetary atmospheres communities. The bulk of my work has involved the measurement and interpretation of high-resolution absorption spectra of vacuum ultraviolet (100-200 nm) and extreme ultraviolet (50-100 nm) transitions. I am also active in the field of Fourier transform spectroscopy of diatomic molecules, and I have a continuing interest in laser spectroscopies of diatomics.

Research Projects:

I. I am involved in a number of laboratory projects focusing on the EUV (extreme ultraviolet) and VUV (vacuum ultraviolet) absorption spectra of diatomic and triatomic molecules of astrophysical interest. I measure and analyze absolute photoabsorption cross sections (or equivalently, transition probabilities or oscillator strengths), line widths, and wavelengths of molecular features that are needed for the interpretation of the photophysics and photochemistry of both astronomical sources and the Earth’s atmosphere. These projects are currently supported by grants to Wellesley College from the NASA Planetary Atmospheres, Origins of Solar Systems, and Astrobiology & Exobiology programs.grant to Wellesley College. Current projects include:

(a) Molecular Nitrogen: I am completing a laboratory project to measure line f-values and widths in the complex N₂ spectrum between 80 and 100 nm. These measurements are incorporated into a theoretical model of the absorption spectrum of N₂ which has established the mechanisms responsible for predissociation and  reproduces the observed features in all N₂ isotopomers as a function of temperature. Measurements are currently being carried out on the DESIRS beamline of the SOLEIL synchrotron facility in St. Aubin, France.

A website has been constructed and is now online, titled N₂ Photoabsorption Cross Sections in the Vacuum Ultraviolet. The site, which resides at Wellesley College, provides access to the outputs of a photoabsorption cross section model developed at the Australian National University (ANU) Research School of Physics and Engineering Atomic and Molecular Physics Laboratories. The cross sections are derived from a coupled Schrödinger equation (CSE) model of the relevant electronic states, developed by Brenton Lewis and colleagues. The model parameters are optimized to reproduce a large experimental database of line positions, oscillator strengths, and line widths. This work is supported by the NASA Planetary Atmospheres program.

(b) Carbon Monoxide: In collaboration with Dr. Jim Lyons at the UCLA IGPP Center for Astrobiology and with Brenton Lewis and colleagues at the ANU, I am studying the extreme ultraviolet photoabsorption spectrum of CO and its isotopologues.The origin and significance of unusual oxygen isotope ratios discovered in early condensates from the solar nebula have been an intriguing puzzle for the past 30 years. It has been recently proposed that isotope-selective photodissociation of CO in the solar nebula or parent molecular cloud is responsible for the oxygen isotope signatures. This theory places constraints on the formation conditions of the solar nebula, and is amenable to testing with accurate photodissociation calculations for CO isotopologues. To evaluate the CO photodissociation theory we are measuring high-resolution photoabsorption cross sections of CO and its isotopologues in the 91.2 to 111.8 nm region. The results of these measurements will be incorporated into radiative transfer calculations of the solar nebula to quantify oxygen isotope fractionation via CO photodissociation. The measurements are being carried out on the DESIRS beamline at SOLEIL. This work is supported by the NASA Origins of Solar Systems program.

(c) Carbon Dioxide: The photodissociation of CO₂ is a fundamental photochemical process in the atmospheres of Mars and Venus. My research, carried out on the DESIRS beamline at SOLEIL centers on the measurement of high resolution cross sections from 87 to 120 nm. I have completed measurements at 295 K and 195 K over the 106 to 120 nm region, and I am currently undertaking new room temperature measurements in the 87 to 106 nm region. This work is supported by the NASA Planetary Atmospheres program.

(d) Diatomic Sulfur: Interpretations of atmospheric (Io, Jupiter) S₂ absorption features are hindered by a complete lack of laboratory cross sections in the ultraviolet. We have begun to quantify the photoabsorption spectrum of S₂ from 200 to 300 nm based on theoretical calculations and laboratory measurements. Coupled-channel calculations are being complemented by measurements of S₂ absorption at high resolution. We have designed an experimental apparatus to produce a stable column of S₂ vapor and are in the planning stages for high-resolution measurements. This work is supported by the NASA Planetary Atmospheres program.

(e) Sulfur Dioxide: In collaboration with colleagues in the Space and Atmospheric Physics Group at Imperial College, London, I provide astronomers with high-resolution cross section data for the complex ultraviolet SO₂ absorption spectrum. Using the Imperial College VUV Fourier transform spectrometer, we have completed and published cross sections from 198 to 325 nm (295 K) and from 199 to 220 nm (160 K). We recently completed work on further low-temperature measurements from 220 to 325 nm. This work is supported by the NASA Planetary Atmospheres program.

(f) Sulfur Dioxide Isotopologues: In collaboration with Dr. Jim Lyons at the UCLA IGPP Center for Astrobiology and Dr. Doug Blackie and Dr. Juliet Pickering at Imperial College, I am measuring, at high resolution, photoabsorption cross sections of several isotopologues of sulfur dioxide: ³²SO₂, ³³SO₂, ³⁴SO₂, and ³⁶SO₂. The cross sections will be used in models of the early earth atmosphere to test the hypothesis that "mass independent fractionation" of sulfur deposits in early rock samples is a marker of the rise of oxygen in the earth's atmosphere. This work is supported by the NASA Exobiology and Astrobiology program.

2. I have collaborated with Professor Robbie Berg and Tom Bauer of the Physics Department to develop a laser cooling and trapping apparatus. In the summer of 2002 I supervised two physics students, Ama Abeberese ('04) and Frannie D'Arcangelo ('03), working on this project. Building on the accomplishments of a number of other students in the lab, Ama and Frannie successfully trapped rubidium atoms and cooled them to a temperature of only a fraction of a degree above absolute zero. Kali Wilson ('04) completed her senior thesis on this project in the 2003-04 academic year. In the summer of 2004, Oana Ivan ('07) and Rebecca Ward (McDaniel College, '06) re-designed our optical and spectroscopy systems to improve the reliability of the trapping apparatus. Sheila Dwyer ('05) completed a senior thesis in the laser cooling lab in 2005. More recently, Liz Rivers ('07), Christina Miller ('08), Rita Lam ('09), and Amila Hadziomerspahic ('10) continued the development of this apparatus.

 Publications

D. Blackie, R. Blackwell-Whitehead, G. Stark, J. C. Pickering, P. L. Smith, J. Rufus, and A. P. Thorne, High-resolution photoabsorption cross-section measurements of SO2 at 198 K from 213 to 325 nm, J. Geophys. Res., 116, E03006, doi:10.1029/2010JE003707 (2011).

J. Rufus, G. Stark, A. P. Thorne, J. C. Pickering, R. J. Blackwell-Whitehead, D. Blackie, and P. L. Smith, High-resolution photoabsorption cross-section measurements of SO₂ at 160 K between 199 and 220 nm, J. Geophys. Res., 114, E06003, doi:10.1029/2008JE003319 (2009).

K. P. Huber, M.-C. Chan, G. Stark, K. Ito, and T. Matsui, N₂ band oscillator strengths at near-threshold energies, J. Chem. Phys. 131, 084301 (2009).

A. N. Heays, B. R. Lewis, G. Stark, K. Yoshino, P. L. Smith, K. P. Huber, and K. Ito, Oscillator strengths and line widths of dipole-allowed transitions in ¹⁴N₂ between 86.0 and 89.7 nm, J. Chem. Phys. 131, 194308 (2009).

X. Liu, D. E. Shemansky, C. P. Malone, P. V. Johnson, J. M. Ajello, I. Kanik, A. N. Heays, B. R. Lewis, S. T. Gibson & G. Stark,Experimental and coupled-channels investigation of the radiative properties of the N₂ c₄^{' 1}S⁺_u - X ¹S⁺_g band system, J. Geophys. Res. 113, A02304 (2008).