Michael J. Berry

F + H2, D2, HD reactions: Chemical laser determination of the product vibrational state populations and the F + HD intramolecular kinetic isotope effect

Relative gain coefficients of individual HF†(DF†) laser transitions in the F + H2, D2, HD chemical lasers have been measured by a grating selection technique. Product vibrational population inversions Nν/Nν−1 were calculated from these measurements. The results indicate a complete parallelism in product vibrational energy content in the four room‐temperature isotopic reactions, modified only by a threshold effect for HF†(ν = 3) production in the F + HD reaction and by secondary mass effects in the HF‐producing VS DF‐producing reactions. A room‐temperature measurement of the intramolecular kinetic isotope effect in the F + HD reaction is reported. Lastly, evidence is presented for highly efficient energy‐transfer processes [V → V′: HF†(ν = 3) + HD(ν = 0) → HF†(ν = 2) + HD†(ν = 1) and E → V: I*(5 2P1/2) + HF†(ν) → I(5 2P3/2) + HF†(ν + 2)].

Golden rule calculation of reaction product vibronic state distributions

Abstract A resonance decay model of bimolecular exchange reactions successfully treats product vibronic state distributions. Product vibronic population inversions are controlled by the extent of product structural change which occurs as reaction energy is released.

CN photodissociation and predissociation chemical lasers: molecular electronic and vibrational laser emissions

Molecular electronic [CN*(A2Π3/2, v′ = 0) → CN(X2Σ+, v″ = 0,1,2)] and vibrational [CN† (X2Σ+, v′) → CN(X2Σ+, v′ − 1), v′ = 5,4,3,2] cyanide radical laser emissions have been observed following photodissociative and predissociative fragmentation of cyanide parents [HCN, ClCN, BrCN ICN, (CN)2, CH3NC, CF3CN, C2F5CN] at λ ≥ 1550 A. The observed transitions and their relative gain coefficients and quenching behaviors are used in connection with spectroscopy and fluorescence experiments to formulate a state‐to‐state photochemical reaction mechanism, viz., RCN lim →ℏ ωR+CN*(A2Πi,v′=0 primarily),CN*(A2Πi,v′=0)+M→ CN†(X2Σ+,v″=4 primarily)+M, in which nascent photochemical products are formed with high electronic population inversion [NCN*(A)/NCN(X) ≫ 1] and no vibronic inversion within the A2Πi manifolds (i.e., v = 0 is the principal product vibronic state). Near‐resonant collision‐induced intersystem crossing is shown to preferentially populate v = 4 within the X2Σ+ electronic manifold. Electronic and vibronic po...

Golden rule calculation of product vibronic population inversions in photodissociation and related reactions

Abstract An ultrasimple reaction dynamics model successfully treats product vibronic state distributions in photodissociation and predissociation reactions and in collision-induced electronic-to-vibrational energy transfer processes. Product vibronic population inversions are determined by intrafragment dynamics (i.e., changes in bond lengths and strengths) which occur during reaction product formation.

Measurement of highly forbidden optical transitions by intracavity cw dye laser spectroscopy

Abstract Intracavity cw dye laser quenching has been used to observe extremely weak optical transitions near 6300 A: the 2.0 band of the red atmospheric system of molecular oxygen and the 6,0 overtone band of HCl. Sensitivity tests indicate that band systems with oscillator strengths less than 10 −2 can be detected readily, thereby suggesting routine use for high-resolution optical spectroscopy of forbidden transitions.

Analysis of electronically nonadiabatic chemical reactions: An information theoretic approach

Abstract A practical procedure for the determination of branching ratios for reactions which lead to either excited or electronically ground state products is outlined. The method is applied to four reactions which could (on energetic grounds) produce an electronically excited iodine atom. No case of a complete inversion is found, but one reaction (F + HI) is predicted to yield a statistical, (one half), I * ( 2 P 1/2 ) to I( 2 P 3/2 ) ratio.

The formyl fluoride photochemical laser: photochemistry and energy content of the HF photoelemination product

Abstract Photolysis (λ > 1650 A) of formyl fluoride (HFCO) leads to HF infrared laser emission. The energy content of the HF photoelemination primary product is only a small fraction (≈ 7%) of the available excess energy. Fluorine atoms may also be produced as primary photochemical products.

Vibronic surprisal analysis of the dynamics of photodissociation and related reactions

Abstract Comparisons of experimentally observed product vibronic state distributions to statistically expected distributions indicate that intrafragment dynamics have primary importance in photodissociative and predissociative excitation reactions and in collision-induced electronic-to-vibrational energy transfer processes and that collisional dissociative excitation reactions probably involve sequential 2-body interactions rather than a concerted 3-body interaction.

ICN photodissociation and predissociation: CN*(A 2Πi) fluorescence excitation spectrum and CN† (X 2Σ+) chemical laser emission☆

New ICN photochemical experiments [viz., observation of CN† (X 2Σ+)_chemical laser emission in the presence of rare gas atom collision partners and determination of the CN* (A 2Πi) fluorescence excitation spectrum] are reported and are used to clarify the mechanism of ICn photodissociation and predissociation in the 1550–2000 A spectral region.

A comparison of photolytic fluorine-atom sources for chemical laser studies

Abstract WF 6 , CF 3 I, CF 2 CFCl, and CF 2 CFBr have been used as photolytic fluorine-atom sources to study the F+H2 chemical laser under identical apparatus and sample conditions. From a comparison of the observed HF laser transitions and from other experiments, WF 6 and, by implication, many other previously used fluorine-atom sources appear to be unsuitable for quantitative chemical laser studies of reaction energy partitioning. In constrast, CF 3 1, CF 2 CFCl, and CF 2 CFBr may be highly suitable for quantitative studies.