Events & Seminars > Event Details


4:00 pm
Room 304, Chemistry Building

Is it just another halogen? Reassuring similarities and surprising differences in the binding to fluorine and chlorine in protic acid-haloethylene complexes


Professors Mark Marshall and Helen Leung
Amherst College

Hosted by: Professors Eric Herbst and Kevin Lehmann

Microwave, rotational spectroscopy of gas-phase molecular heterodimers is a powerful method for determining the structures of these species.  Comparisons among the geometries adopted in a series of analogous complexes provide information regarding the nature of intermolecular interactions.  Complexes formed between protic acids and fluoroethylenes adopt similar structures that can be explained in terms of familiar chemical concepts.  But replacing a fluorine atom by a chlorine atom, while sometimes having little effect, in other examples will lead instead to significant structural changes.  These include distinctly different modes of bonding in complexes formed by vinyl chloride with hydrogen fluoride, hydrogen chloride, and acetylene, respectively, and a preference for binding to chlorine, not fluorine, in (Z)-1-chloro-2-fluoroethylene-acetylene.  The structures of several analogous complexes are examined in an attempt to provide insight into the factors governing the intermolecular interactions in these species.


Mark Marshall was born in Connecticut and was raised in the southeastern portion of that state, which was quite rural at the time.  He received his B.S. in Chemistry at the University of Rochester in 1979, where he performed undergraduate research with John S. Muenter.  He then entered graduate school at Harvard University, where he received both an M.A. (1981) and a Ph.D. (1985) working with William Klemperer probing molecular potential energy surfaces though applications of high resolution far infrared and microwave spectroscopy.  After two years as a Research Associate at the Herzberg Institute of Astrophysics of the National Research Council Canada in Ottawa, he joined the faculty of Amherst College in 1987 where he is now the Class of 1959 Professor of Chemistry.  He has held visiting appointments at the University of North Carolina, the University of Rochester, and the University of Pennsylvania.

Helen Leung was born in Hong Kong, where she began her education.  After a final year of secondary education in Weybridge, England, she attended the California State University, Northridge where she received both a B.S. in Chemistry (1982) and a B.A. in Biology (1983).  She continued to graduate school at Harvard University for an M.A. (1985) and Ph.D. (1988), where she worked with William Klemperer on experimental and theoretical studies of weakly bound molecules.  Helen spent three years at the Harvard-Smithsonian Center for Astrophysics as a post-doctoral fellow for Patrick Thaddeus and Alex Dalgarno, primarily using microwave spectroscopy to map star-forming regions in Cygnus X.  She started her academic career as a visiting professor at Williams College in 1991, followed by a tenure-track position at Mount Holyoke College in 1993, receiving tenure in 1998.  In 2002, she relocated to Amherst College where she is now the George H. Corey 1888 Professor of Chemistry.  She has held a visiting appointment at the University of Pennsylvania.

At Amherst College, Professors Leung and Marshall and their undergraduate students investigate intermolecular interactions through structural characterization of weakly bound, gas-phase molecular heterodimers via microwave spectroscopy and applications of quantum chemistry calculations.