A Spectroscopist's View of Energy States, Energy Transfers, and Chemical Reactions

Abstract

This chapter describes a research career beginning at Berkeley in 1960, shortly after Sputnik and the invention of the laser. Following thesis work on vibrational spectroscopy and the chemical reactivity of small molecules, we studied vibrational energy transfers in my own lab. Collision-induced transfers among vibrations of a single molecule, from one molecule to another, and from vibration to rotation and translation were elucidated. My research group also studied the competition between vibrational relaxation and chemical reaction for potentially reactive collisions with one molecule vibrationally excited. Lasers were used to enrich isotopes by the excitation of a predissociative transition of a selected isotopomer. We also tested the hypotheses of transition-state theory for unimolecular reactions of ketene, formaldehyde, and formyl fluoride by (a) resolving individual molecular eigenstates above a dissociation threshold, (b) locating vibrational levels at the transition state, (c) observing quantum resonances in the barrier region for motion along a reaction coordinate, and (d) studying energy release to fragments. GETTING STARTEDI had the good fortune to grow up on a farm in eastern Pennsylvania, where hard work produced good crops, poultry, and livestock; where I could help my father take apart, repair, and reassemble farm equipment; and where I could manufacture and experiment with gun powder. In those days, parents could still give chemistry sets to their children, and the East Coast sky was often clear enough to observe shooting stars while lying flat on the bed of a hay wagon. This constituted my first spectroscopic observations of chemistry in action. My initial in-class chemistry lab was a study of sulfur combustion carried out by placing a fumigation candle in the ink well of my third-grade desk and lighting it on departure for recess. This early initiative was not encouraged on my return from the playground. One of Princeton Professor Hubert Alyea's renowned lectures on the marvels of chemistry at a nearby high school provided my first look at cryogenics as he exhaled through a mouth full of dry ice. By the time I finished a series of integrated courses in the physical sciences, a one-week visit by J. Robert Oppenheimer, and a challenging course in analytical/inorganic chemistry in high school (Phillips Exeter Academy in New Hampshire), I was well on my way to becoming a physical chemist. The launching of Sputnik during my first month of college (October 1957) at Harvard sharply increased federal funding for scientific research and greatly encouraged scientific career paths. That fall, the intensity of lab courses in physics and organic chemistry, a fourth-semester calculus course, and a humanities course quickly ended my aspiration to extend my high-school crew experience to intercollegiate rowing. A series of research projects in Paul D. Bartlett's personal lab at Harvard and summer jobs at Arthur D. Little and General Electric's corporate research lab deepened my interest and experi...

Chirped-pulse millimeter-wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions

“…At room temperature, T wall = 300 K, acetaldehyde has T rot = 3.5 K. We conclude that molecular rotations of acetaldehyde expanded from this heated Chen nozzle are effectively thermalized to the translational temperature of the carrier gas. This conclusion is consistent with the consensus in the literature 63 that rotational degrees of freedom are cooled efficiently in the supersonic expansion. Indeed, the typical translational temperature of the carrier gas of several Kelvins is close to the energy spacing between the rotational levels of most molecules and efficient relaxation of highly excited rotational levels is possible.…”

Exploring Multiple Potential Energy Surfaces: Photochemistry of Small Carbonyl Compounds

“…It was suggested experimentally that the photodissociation of H 2 CO at low-photon energies occurs on the S 0 PES after an internal conversion (IC) from the S 1 PES [61][62][63][64][65]. Hence, dynamics as well as stationary points on the ground state S 0 PES have been studied extensively by theoretical calculations [39,40,[43][44][45].…”

Photochemistry of Methyl Ethyl Ketone: Quantum Yields and S1/S0‐Diradical Mechanism of Photodissociation

“…The photodissociation mechanism of the smallest aldehyde, formaldehyde, has been studied extensively by theoretical calculations. Since its decomposition had been postulated to take place on the ground state PES after an S 1 to S 0 nonadiabatic transition,31 exploration for dynamics32–34 as well as stationary points35–38 on the S 0 PES have been the subjects of most theoretical studies. In the last two years, the nonadiabatic decay mechanisms were revealed in detail by Morokuma et al13, 39–41 and Robb et al42, 43 A new T 1 /S 0 crossing seam has recently been discovered inside the potential well of formaldehyde,13, 41 which has provided an answer to a long‐standing mystery in the low energy photolysis how the S 0 species can be generated inside the potential well before the S 0 dynamics.…”