ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfrared multiphoton decomposition and energy-dependent absorption cross section of chloroethaneJoseph S. Francisco, Warren D. Lawrance, Jeffrey I. Steinfeld, and Robert G. GilbertCite this: J. Phys. Chem. 1982, 86, 5, 724–728Publication Date (Print):March 1, 1982Publication History Published online1 May 2002Published inissue 1 March 1982https://pubs.acs.org/doi/10.1021/j100394a027https://doi.org/10.1021/j100394a027research-articleACS PublicationsRequest reuse permissionsArticle Views45Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
Two instrumentation facilities for laser-related research in physical sciences and biomedicine are in operation at the MIT Spectroscopy Laboratory. This article describes their organization, resources and performance.
The fluorescence excited in iodine by the green emission line of mercury, in the presence of foreign gases, has been examined by high-resolution photoelectric photometry. Cross sections for quenching, vibrational, and rotational energy transfer for the v′ = 25, J′ = 34 level of the B 3Π0u+ state of iodine have been obtained, for collisions with 3He, 4He, Ne, Ar, Kr, Xe, H2, O2, CO2, SO2, CH3Cl, and NH3. Emission bands have been rotationally analyzed to yield partial total cross sections for the inelastic processes. These have been corrected for multiple scattering by a computer simulation procedure. The correlation of quenching efficiency with the mass and polarizability of the collision partner, found by Brown for the quenching of the v′ = 15 level of iodine, holds for the v′ = 25 level as well. There is no contribution to quenching efficiency from a permanent electric dipole moment. The data suggest that a complex set of interactions, including electrostatic polarization, spin—orbit forces, and specific chemical effects, are responsible for quenching, indicating a multiplicity of repulsive states contributing to the induced predissociation process. The vibrational energy-transfer efficiency is maximum when the mean collision time equals the period of oscillation of the molecule, which corresponds to a collision reduced mass ≃40 for T = 370°K, v′ = 25 of I2; vibrational transfer is largely independent of the internal structure of the collision partner. The efficiency of pure rotational energy transfer (Δv′ = 0) shows a similar smooth dependence on reduced mass of the collision system, with the exception of the molecules SO2, CO2, and CH3Cl, which are more efficient. Quantitative measurements have been made on partial components of total inelastic cross sections for ΔJ′ up to ±20 angular momentum units, with evidence for a total spread of ΔJ′ up to 30 or 40. The width of the distribution of partial cross section components decreases in the order Δv′=+2>−2≳+1>−1≫0; also, the ΔJ′ distribution is broader for collisions with heavier particles.
A time-resolved infrared double-resonance technique has been used to measure vibrationally and rotationally inelastic collision rates in ground and vibrational overtone levels of methane. A Raman-shifted Ti:sapphire laser is used to pump J=0 through 7 states in the 2ν3 and ν3+ν4 levels of 12CH4, and a tunable diode laser is used to probe the time-dependent level populations. Vibrational equilibration is observed among the octad, pentad, and dyad levels, with subsequent relaxation to the ground state. State-to-state rotational energy transfer rates are obtained in the ground and ν3+ν4 excited vibrational levels, and compared with theoretical predictions and with pressure-broadening measurements on the corresponding transitions. The probability of molecular reorientation in an inelastic collision is also inferred from the polarization dependence of the relaxation times. Parity-conserving and vibrational angular momentum propensity rules are inferred for the lower rotational levels of methane.
We have used a time-resolved double-resonance (pump-probe) method to assign the CHD 3 spectra taken by an FT-IR spectrometer at high resolution. The spectra of 2ν 3 , ν 3 + ν 6 , and 2ν 6 around 2000 cm −1 were investigated. Collisional processes in the molecule were investigated by the time evolution of the signal and double-resonance spectra.
