Infrared lasers in chemistry

John, Phillip

doi:10.1021/ed059p135

Cited by 2 publications

(1 citation statement)

References 4 publications

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“…Absorption of a single infrared photon produces a vibrationally excited molecule with insuffficient energy to undergo chemical transformation. With the advent of high powered infrared lasers, it has become possible to effect chemical reactions via multiphoton absorption in an intense laser field (1)(2)(3)(4). Thus laser technology has spawned a new field of chemistry, infrared photochemistry.…”

Section: Introductionmentioning

confidence: 99%

Infrared multiphoton isomerization and fragmentation reactions of organic molecules

Lewis¹,

Buechele²,

Teng³

et al. 1982

Pure and Applied Chemistry

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-The tunability of the CO2 molecular gas laser permits selective multiphoton infrared excitation of one isomer in a mixture of isomers. This capability can be exploited to drive isomerization reactions in a contrathermodynamic direction. Examples of such reactions are the trans + cis isomerization of alkenes and the electrocyclic isomerization of butadienes to cyclobutenes. It is also possible to achieve some selectivity in consecutive isomerization reactions (A + B + C) and in competing reactions (A + B ÷ C) via multiphoton infrared excitation. For example, consecutive reactions can be stopped at the intermediate product B in cases where the activation energy for B + C is lower than that for A + B. The product ratio B/C in competing reactions is, in some cases, dependent upon the average vibrational temperature of the reactant A and hence can be altered by changing laser fluence or collisional frequency. In addition, pulsed infrared lasers can be used to create high concentrations of vibrationally excited fragmentation products. We are currently seeking to correlate product vibrational energy distributions with reactant structure and decomposition mechanism. INTRODUCT IONReactions of electronically excited polyatomic organic molecules have occurred on earth since the prebiotic era and have been the subject of scholarly publications since the emergence of the modern chemical literature. All photochemists are familiar with the Stark-Einstein law: electronic excitation occurs upon absorption of a single quantum of light. Under the best of circumstances, the electronically excited molecule can undergo chemical transformation with unit efficiency. Absorption of a single infrared photon produces a vibrationally excited molecule with insuffficient energy to undergo chemical transformation. With the advent of high powered infrared lasers, it has become possible to effect chemical reactions via multiphoton absorption in an intense laser field (1-4). Thus laser technology has spawned a new field of chemistry, infrared photochemistry. From a historical perspective it is interesting to note that the initial investigations of photochemical mechanisms were conducted in the vapor phase (5). Chemical applications of infrared lasers have thus far been limited almost exclusively to the vapor phase. THE CO2 LASERThe commonly used source for infrared laser chemistry is the pulsed CO2 molecular gas laser. The important characteristics of the CO2 laser are (a) high power (ca. 1020 photons/pulse or several gigawatts/cm2 in a focused beam), (b) moderately short pulse duration (< 1 is), and (c) limited tunability from ca. 907 to 992 cm1 and from 1016 to 1092 cm1. Its high power makes the CO2 laser well suited for many technological (welding, cutting, etc.) as well as chemical applications. Thesimplest chemical application of CO2 lasers is the uniform heating of the irradiated volume either by direct absorption 1683

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Section: Introductionmentioning

confidence: 99%

Infrared multiphoton isomerization and fragmentation reactions of organic molecules

Lewis¹,

Buechele²,

Teng³

et al. 1982

Pure and Applied Chemistry

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Selective isomerization of alkenes, dienes, and trienes with infrared lasers

Lewis¹,

Weitz²

1985

Acc. Chem. Res.

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Unimolecular isomerization reactions of unsaturated hydrocarbons have been a fertile research field for nearly a century.1 In 18912 Skraup reported that cistrans isomerization of maleic acid occurred upon heating, while the Claisen and Cope rearrangements date from 19123 and 1939,4 respectively. Other now familiar electrocyclic and sigmatropic reactions provide the experimental foundation upon which the theory of pericyclic reactions of Woodward and Hoffman5 was based. This theory in turn kindled interest in both concerted and nonconcerted thermal isomerization reactions of hydrocarbons.Kistiakowsky's6 series of papers on cis-trans isom-

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Infrared lasers in chemistry

Abstract: Summarizes the important details of infrared laser chemistry, particularly the consequences of differences between thermal and laser induced multiple photon dissociation.

Cited by 2 publications

References 4 publications

Infrared multiphoton isomerization and fragmentation reactions of organic molecules

Infrared multiphoton isomerization and fragmentation reactions of organic molecules

Selective isomerization of alkenes, dienes, and trienes with infrared lasers

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