High‐resolutionRaman Spectroscopy of Gases

Abstract

A review of high‐resolution Raman spectroscopy of gases, including spontaneous, incoherent Raman spectroscopy, as well as of nonlinear techniques for coherent anti‐Stokes scattering (CARS), stimulated Raman gain (SRG) and stimulated Raman loss (SRL) spectroscopy, and photoacoustic Raman spectroscopy (PARS) in the frequency domain is presented. Femtosecond degenerate four‐wave mixing spectroscopy (Fs‐DFWM) and Raman‐induced polarization spectroscopy (RIPS) in the time domain are discussed. Also treated are the broadenings of Raman lines due to the Doppler and pressure effects. Basic theoretical notions and working equations for the analysis of highly resolved spectra are presented. Examples are drawn from the literature to illustrate the respective advantages and disadvantages of the various techniques. The interplay between high‐resolution Raman spectroscopy, infrared spectroscopy, and ab initio computational schemes is illustrated. The article concludes with an overall assessment of the respective advantages and disadvantages of the methods used in high‐resolution Raman spectroscopy.

Probing the Structure, Pseudorotation, and Radial Vibrations of Cyclopentane by Femtosecond Rotational Raman Coherence Spectroscopy

“…Prior to each RCS experiment, the experimental apparatus function G ( t ) is measured via the zero time Kerr peak of Ar gas. The stimulated Raman response of the medium to the three laser pulses is described by the third-order susceptibility χ (3) ( t ), which can be modeled for t > 0 as where C is a proportionality constant and b J , K ,ν is an amplitude coefficient that includes the rotational and vibrational level population factors, the rotational ( g J , K ) and vibrational ( g ν ) degeneracies, nuclear spin statistics, and the rotational Raman intensity coefficients for anisotropic Raman scattering (Placzek–Teller factors). − The Δω J , K ,ν in eq are the frequencies of all rotational Raman-allowed transitions from states with rotational quantum numbers J , K and vibrational quantum number ν that can undergo stimulated Raman transitions within the femtosecond laser bandwidth of ∼100 cm –1 . While the classical bent and twist equilibrium geometries are asymmetric, the vibrational ν = 0 level is delocalized over all 20 stationary points (see Figure ), which renders cyclopentane an effective symmetric top molecule.…”

Rotational constants and structure of para-difluorobenzene determined by femtosecond Raman coherence spectroscopy: A new transient type

“…However, compared to the treatments of the symmetric top molecules TFB and HFB, the asymmetric-top Raman RCS simulations are significantly more involved: First, the asymmetric-top rotational eigenfunctions and energy eigenvalues E(J, K 1 , K −1 ) must be computed numerically, in contrast to symmetric tops whose rotational level energies can be expressed analytically. Second, the rotational Raman transition intensities of symmetric tops are given analytically by the Placzek-Teller factors, 4,5 which involve only a few multiplication and division operations, while for asymmetric tops, the evaluation of the rotational Raman intensities involves ∼J 3 floating-point operations. 4 Third, the three different diagonal (in some cases also off-diagonal) components of the molecular polarizability tensor of asymmetric-top molecules give rise to different rotational transient types.…”

Cavity-enhanced Raman spectroscopy with optical feedback cw diode lasers for gas phase analysis and spectroscopy

“…Promising Raman detection schemes are based on the stimulated Raman method, including inverse Raman spectroscopy, coherent anti-Stokes Raman spectroscopy (CARS), or photoacoustic stimulated Raman spectroscopy (PARS). [1][2][3][4] However, these techniques involve complex arrangements and require two different wavelengths from high power lasers.…”