High Resolution Infrared Studies of Molecular Dynamics

Hirota, Eizi; Kawaguchi, Kentarou

doi:10.1146/annurev.pc.36.100185.000413

Cited by 49 publications

(5 citation statements)

References 77 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Assuming an extinction coefficient" in the range (3)(4)(5)(6) x lop3 dm3 mol-' cm-' for the i.r. band of B, we calculate a value of (2)(3)(4) x lo9 dm3 mol-' s-l for recombination of B in cyclohexane solution:…”

Section: Resultsmentioning

confidence: 99%

Apparatus for fast time-resolved infrared dectection of reaction intermediates in the solution photochemistry of transition-metal carbonyls

Dixon¹,

Healy²,

Hodges³

et al. 1986

J. Chem. Soc., Faraday Trans. 2

View full text Add to dashboard Cite

An apparatus is described for time-resolved i.r. spectroscopy of metal carbonyls in solution, based on a C.W. CO laser for i.r. spectroscopy and either a U.V. excimer laser or an Xe flash lamp for photolysis. Typical performance data are: tuning range, 2020-1700m-' (tunable in steps of 4cm-'); i.r. detection risetime, 700 ns; sensitivity, an absorbance change of lop3 can be detected with an S I N ratio of 5 on single shot. These specifications are supported by results from the photochemistry of [ (C5H5)Fe(C0)J2 in cyclohexane solution, including high-pressure experiments and dual-wavelength photolysis.

show abstract

Section: Resultsmentioning

confidence: 99%

Apparatus for fast time-resolved infrared dectection of reaction intermediates in the solution photochemistry of transition-metal carbonyls

Dixon¹,

Healy²,

Hodges³

et al. 1986

J. Chem. Soc., Faraday Trans. 2

View full text Add to dashboard Cite

show abstract

“…Additionally, the authors anticipate that an area for future research with great potential is optical pump, THz probe spectroscopy. Time-resolved infrared measurements using a variety of experimental techniques − have provided a wealth of information on molecular dynamics, but none of these methods are capable of the time resolution in the far-infrared of THz-TDS. To perform a time-resolved THz-TDS study, an optical pump beam would cause photoexcitation, photolysis, or photodissociation of a sample and the resulting rotational distribution would be probed with subpicosecond resolution.…”

Section: Discussionmentioning

confidence: 99%

Terahertz Studies of Collision-Broadened Rotational Lines

1997

View full text Add to dashboard Cite

Via terahertz (THz) coherent transients and THz time-domain spectroscopy, we have measured the far-wing absorption line profile of the ensembles of collision-broadened ground state rotational lines of methyl bromide, methyl chloride, and methyl fluoride vapors out to more than 200 line widths from resonance, corresponding to frequency offsets as much as 5 times the resonant frequency. On these far wings the measured absorption is approximately an order of magnitude less than that predicted by the van Vleck−Weisskopf theory. Our observations show that as the offset frequency is increased, a transition occurs from the regime of the van Vleck−Weisskopf theory to the regime of the Lorentz theory. These measurements are fit to a new molecular response theory which explicitly includes the molecular orientation time during a collision. Due to the broad bandwidth of the THz pulses, we demonstrate the validity of this molecular response theory for the far-wing absorption of methyl fluoride, chloride, and bromide. The excellent theoretical fit to our measurements encompassing the frequency range over which this transition occurs indicates a molecular response time on the order of 200 fs. These measurements also permit determination of the line-width dependence on the rotational quantum number J.

show abstract

“…In addition, the detection of low molecular weight transient species, such as radicals and molecular ions, is of key importance because they govern most of the chemical and kinetic processes in plasmas. Over the last two decades, chemical sensing using mid infrared laser absorption spectroscopy (MIR-LAS) in the molecular fingerprint region from 3 to 20 μm has been established as a powerful in situ diagnostic tool for molecular plasmas [1][2][3][4][5]. The methods of MIR-LAS provide a means to measure molecular species concentrations in the ground state and the temperature of reactive species.…”

Section: Introductionmentioning

confidence: 99%

On the application of cw external cavity quantum cascade infrared lasers for plasma diagnostics

Lopatik¹,

Lang²,

Macherius³

et al. 2012

Meas. Sci. Technol.

View full text Add to dashboard Cite

Three continuous wave external cavity quantum cascade lasers (EC-QCLs) operating between 1305 and 2260 cm −1 (4.42-7.66 μm) have been tested as radiation sources for an absorption spectrometer focused on the analysis of physical and chemical phenomena in molecular plasmas. Based on the wide spectral tunability of EC-QCLs, multiple species detection has become feasible and is demonstrated in a study of low-pressure Ar/N 2 microwave plasmas containing methane as a hydrocarbon precursor. Using the direct absorption technique, the evolution of the concentrations of CH 4 , C 2 H 2 , HCN and H 2 O has been monitored depending on the discharge conditions at a pressure of p = 0.5 mbar and at a frequency of f = 2.45 GHz in a planar microwave plasma reactor. The concentrations were found to be in the range of 10 11 -10 14 molecules cm −3 . In addition, based on the analysis of the line profile of selected absorption lines, the gas temperature T g has been calculated in dependence on the discharge power. T g increased with the power values and was in the range between 400 and 700 K. Further, in a pure He/Ar microwave plasma, the wavelength modulation spectroscopy technique has been applied for the sensitive detection of transient plasma species with absorbencies down to 10 −5 . The typical spectral line width of an EC-QCL under the study was found to be in the range 24 to 38 MHz depending (i) on the chopping technique used and (ii) on a single or averaged measurement approach. Further, different methods for the modulation and tuning of the laser radiation have been tested. Varying the power values of an EC-QCL between 0.1 and 154 mW for direct absorption measurements under low pressure conditions, no saturation effects in determining the concentrations of methane, acetylene and carbon monoxide could be found under the experimental conditions used, i.e. for lines with line strengths between 10 −19 and 10 −22 cm molecule −1 .

show abstract

High Resolution Infrared Studies of Molecular Dynamics

Cited by 49 publications

References 77 publications

Apparatus for fast time-resolved infrared dectection of reaction intermediates in the solution photochemistry of transition-metal carbonyls

Apparatus for fast time-resolved infrared dectection of reaction intermediates in the solution photochemistry of transition-metal carbonyls

Terahertz Studies of Collision-Broadened Rotational Lines

On the application of cw external cavity quantum cascade infrared lasers for plasma diagnostics

Contact Info

Product

Resources

About