Formaldehyde Photochemistry

Moore, C. Bradley; Weisshaar, J C

doi:10.1146/annurev.pc.34.100183.002521

Cited by 259 publications

(148 citation statements)

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“…The attempt to observe rovibrational energy transfers in the excited state of a polyatomic led us into a long study of radiationless transitions and unimolecular reaction dynamics in formaldehyde (96)(97)(98). It was fortunate for me that during the first half of these years I learned tenacity from Joel Hildebrand (99) …”

Section: Unimolecular Reactions Formaldehydementioning

confidence: 99%

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

Moore

2007

Annu. Rev. Phys. Chem.

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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...

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Section: Unimolecular Reactions Formaldehydementioning

confidence: 99%

“…The transition state geometry and reaction coordinate are shown (107 (96,98); thus I present only a few highlights here.…”

Section: Figurementioning

confidence: 99%

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

Moore

2007

Annu. Rev. Phys. Chem.

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“…In remote oceanic areas (Wagner et al, 2002;Weller et al, 2000), in the free troposphere (Frost et al, 2002), and in the stratosphere, only the photochemical oxidation of CH 4 serves as the major source. Apart from the importance of the rather simple CH 2 O molecule in the Earth's atmosphere and far beyond, it is also subject to fundamental research regarding for instance the exact processes during its photolysis (e.g., Moore and Weisshaar, 1983;Townsend et al, 2004;Troe, 2007).…”

Section: Introductionmentioning

confidence: 99%

Hydrogen isotope fractionation in the photolysis of formaldehyde

2008

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Abstract. Experiments investigating the isotopic fractionation in the formation of H 2 by the photolysis of CH 2 O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in the H 2 produced is 500(±20)‰ with respect to the parent CH 2 O. We also observed that complete photolysis of CH 2 O under atmospheric conditions produces H 2 that has virtually the same isotope ratio as that of the parent CH 2 O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH 2 O+hν→CHO+H) as compared to the molecular channel (CH 2 O+hν→H 2 +CO) of the photolysis of CH 2 O in order to balance the relatively small isotopic fractionation in the competing reaction of CH 2 O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08), which is equivalent to a 780(±80)‰ enrichment in D of the remaining CH 2 O. When CH 2 O is in photochemical steady state, the isotope ratio of the H 2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H 2 (α m ) but also by overall fractionation for the removal processes of CH 2 O (α f ), and is represented by the ratio of α m /α f . Applying the isotopic fractionation factors relevant to CH 2 O photolysis obtained in the present study to the troposphere, the ratio of α m /α f varies from ∼0.8 to ∼1.2 depending on the fraction of CH 2 O that reacts with OH and that produces H 2 . This range of α m /α f can render the H 2 produced from the photochemical oxidation of CH 4 to be enriched in D (with respect to the original CH 4 ) by the factor of 1.2-1.3 as anticipated in the literature.

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“…As a result, the transition strength is approximately six orders of magnitude smaller than common values for electronically allowed transitions, hindering depopulation of a lower state and increasing the absorption length by the same amount. Second, thẽ A 1 A 2 state predissociates causing it to have a lifetime of slightly less than 10 ns [13]. The correspondingly large linewidth further complicates depopulation by diluting available laser power.…”

Section: Experimental Methodsmentioning

confidence: 99%

Doppler-free spectroscopy of weak transitions: An analytical model applied to formaldehyde

et al. 2007

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Experimental observation of Doppler-free signals for weak transitions can be greatly facilitated by an estimate for their expected amplitudes. We derive an analytical model which allows the Doppler-free amplitude to be estimated for small Doppler-free signals. Application of this model to formaldehyde allows the amplitude of experimentally observed Doppler-free signals to be reproduced to within the experimental error.

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Formaldehyde Photochemistry

Cited by 259 publications

References 47 publications

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

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

Hydrogen isotope fractionation in the photolysis of formaldehyde

Doppler-free spectroscopy of weak transitions: An analytical model applied to formaldehyde

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