Femtosecond Broadband Absorption Spectroscopy of Fragments Formed in the Photodissociation of Gas‐Phase Molecules

Glownia, J. H.; Walkup, R. E.; Gnass, D. R.; Kaschke, M.; Misewich, J.; Sorokin, P. P.

doi:10.1002/9783527619436.ch3

Cited by 2 publications

(3 citation statements)

References 29 publications

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“…These results establish the applicability of fs DFWM to the study of reactions. It is worth noting that the IBM group has observed the steps (and not the resonance) in the absorption detection approach . Although DFWM is basically an absorption technique, its background-free and sensitivity features are very important for this type of application.…”

Section: Applicationsmentioning

confidence: 99%

“…The fs probing and signal detection mechanism can be realized in various ways. These include, for probing, the methodology of laser-induced fluorescence (LIF), − absorption, mass spectrometry with multiphoton ionization (MPI), ,− photoelectron kinetic energy and ZEKE, and stimulated emission pumping . Nonlinear optical four-wave-mixing (FWM) techniques, like degenerate FWM (DFWM), provide an additional and significant probing method, especially for generalization of absorption techniques in gas-phase reaction dynamics.…”

Section: Introductionmentioning

confidence: 99%

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Femtosecond Real-Time Probing of Reactions. 19. Nonlinear (DFWM) Techniques for Probing Transition States of Uni- and Bimolecular Reactions

1996

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Degenerate four-wave mixing (DFWM), using ∼60 femtosecond (fs) laser pulses, is introduced to study transition-state dynamics of chemical reactions in the gas phase. The ultrafast techniques are applied to a range of systems, atomic, unimolecular, and bimolecular. It is shown how fs DFWM can be incorporated in different temporal pulse schemes to extract the dynamics. The DFWM beams are configured in a folded boxcar geometry, producing a spatially separated, background-free, femtosecond signal pulse. Aspects of the technique, such as absorption, are investigated. We have taken advantage of the relatively broad spectral width of the fs pulses and extended the techniques to two-color grating experiments in the gas phase. The unimolecular system, NaI, provided a means of testing this new approach. Our experimental observations of the wave packet motion are in excellent agreement with results obtained using laser-induced fluorescence (LIF). A control experiment was also performed on this system, demonstrating the advantages of the nonlinear technique. Bimolecular reactions were initiated for the system Na+H 2 . Atomic sodium was investigated with fs DFWM and the oscillatory wave packet behavior (2 ps period) was observed, corresponding to the fine structure splitting of the 3p level (17.2 cm -1 ). We also explored the application of fs DFWM to the reactive and nonreactive collisions of the Na+H 2 system, which serves as a good model for studying dynamics of nonadiabatic quenching processes and collision complexes.

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Section: Applicationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Femtosecond Real-Time Probing of Reactions. 19. Nonlinear (DFWM) Techniques for Probing Transition States of Uni- and Bimolecular Reactions

1996

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“…We feel that these beams, which can he generated at almost any wavelength in the visible and near UV by the same technique, would make excellent probe beams for femtosecond transient absorption studies of pholodissociation[3].SPIE Vol. 2116/209 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 07/03/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx…”

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confidence: 98%

<title>Recent developments in VUV femtosecond pulse generation: proposal for a higher efficiency F2 (157-nm) laser</title>

Glownia

Gnass²,

Sorokin

1994

SPIE Proceedings

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The efficiency of the four-wave mixing (2w1 -(1)2), VUV ferntosecond source described by us last year (SPIE Vol. 1861) inherently relies UOfl a two-photon resonance enhancement occurring (in Xe gas) when 2 248.5 nrn. Ilowever, it also depends upon the spatial and temporal coherence properties of the input pulses. Development of a new source for producing beams at w with greatly improved coherence properties is here reported. Performance of the four-wave mixiig source with these 'i pulses is described. lerntosecond VUV P1lsCS with energies as high as 60 1J are generated. As a separate topic, we propose the use of a pulsed (nanosecond) infrared laser to deplete the terminal state of an ( 57-nm) laser in order to greatly enhance its performance.(I) 60-12J Femtosecond VUV Pulse (;elerafi.)n A practical method of generating femtosecond-tiine-scale pulses in the spectral range 6 -8.5 cY was discussed in Ref. I. This method is based upon four-wave, difference-frequency (w3 2 (1)1 -(1)2) mixing in Xe. It was shown in [1] that one can utilize a two-photon resonance in Xe to increase the VUV output energy by almost two orders of magnitude (over the output generated in a non-resonant four-wave mixing scheme, such as the OflC employed in Ref. 2) by choosing the beam at O)j to be a Kr1-excimer-amplified (5.0 eV) femtosecond pulse. The Xe energy levels responsihie for the resonant. enhancement in this scheme are shown in Fig. 1. Even with the use of 300-fs, 5.0-eV pulses having less-than-optimal coherence properties (as briefly discussed in Ref. 1, and as more fully described in Ref. 3), this resonantly-enhanced mixing process was utilized to generate 4-1i..J, femtosccond-time-scale, pulses at 1 56 urn, with w2 -f (1)3 energy conversion efliciencics 0.03. It was our original intent to use these seed pulses to test the ultrafast amplificatK)fl characteristics of an P2-discharge [I]. however, the attempts we subsequently made to measure single-pass gain in an l72-discharge (one capable of producing 14 mJ output when operated as a standard nanosecond-time-scale laser) gave only ambiguous results leading us to propose the

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Femtosecond Broadband Absorption Spectroscopy of Fragments Formed in the Photodissociation of Gas‐Phase Molecules

Cited by 2 publications

References 29 publications

Femtosecond Real-Time Probing of Reactions. 19. Nonlinear (DFWM) Techniques for Probing Transition States of Uni- and Bimolecular Reactions

Femtosecond Real-Time Probing of Reactions. 19. Nonlinear (DFWM) Techniques for Probing Transition States of Uni- and Bimolecular Reactions

<title>Recent developments in VUV femtosecond pulse generation: proposal for a higher efficiency F2 (157-nm) laser</title>

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