P. Cancio

Vibrational–torsional coupling. High‐resolution stimulated Raman spectrum of the ν3 band of ethane (12C2H6)

We report a stimulated Raman spectrum of the Q branch of the ν3 band of ethane recorded with a resolution of about 0.0055 cm−1 and an absolute wave‐number accuracy of the order of 0.001 cm−1. This spectrum is analyzed in terms of a vibrational–torsional coupling Hamiltonian that allows for the calculation of the observed wave numbers within the experimental uncertainty. The following spectroscopic parameters (in cm−1) have been obtained: ν30=994.1108(10), B3A1s−B0=−0.006 165(3), B3E3d−B0=−0.006 170(2), B3E3s−B0 =−0.006 184(2), B3A3d−B0=−0.006 257(2), A3A1s−A0=−0.003 037(15), A3E3d−A0 =−0.003 040(12), A3E3s−A0=−0.003 054(12), and A3A3d−A0=−0.003 065(12). A strong dependence of the threefold torsional potential barrier with respect to the q3 normal mode, ∂V3/∂q3=−275.9±1.4 cm−1, is deduced from the present analysis.

High resolution Raman spectroscopy from vibrationally excited states populated by a stimulated Raman process: 2ν2–ν2 of 12C2H2 and 13C2H2

A generalization of a previously reported technique for investigating vibrationally excited states via high resolution Raman spectroscopy is proposed. In a first step, a vibrational state, typically not accessible by a dipole moment transition from the ground state, is populated in a pulsed stimulated Raman process. After a delay of several nanoseconds, a high resolution spectrum corresponding to transitions from this long lived state is recorded following a quasi-cw stimulated Raman spectroscopy scheme. The use of a pulsed dye laser for providing one of the pumping radiations overcomes some of the limitations of the previously proposed scheme, where this radiation was generated by a Raman shifter filled at relatively high pressure with the gas under study. Experimental aspects are discussed and the spectra of the Q branches of 2ν2(Σg+)–ν2(Σg+) of 12C2H2 and 13C2H2 are presented. The analysis of the measured transitions yielded accurate values of the spectroscopic parameters for the v2=2 vibrationally exc...

The ν1 band of ketene

Infrared and Raman spectra of the ν1 band of ketene, H2CCO, have been recorded at Doppler resolution. The infrared spectrum has been obtained with a difference frequency infrared spectrometer, and the Raman spectrum of the Q branches of this band has been recorded using a stimulated Raman spectrometer. The vib‐rotational analysis of the data is very complicated because of many crossings with other vibrational states, which can interact with v1=1 through Fermi or Coriolis mechanisms. We present a discussion on global and local resonances, and we are able to extract information on the perturbing levels and on the perturbation parameters, even though the perturbing bands are not always detected in the spectrum.

High-resolution q-cw SRS spectrum of 12CH4 in the region of the level crossing between ν1 and ν2 + ν4

Abstract Wavenumbers and relative peak heights of 62 peaks observed in the high-resolution “quasi-continuous wave Stimulated Raman Scattering” (q-cw SRS) spectrum of the 12CH4 molecule are reported for the first time. These peaks are assigned mainly to transitions with J values between 10 and 17 of the Q branch of ν1 and ν2 + ν4 bands. A comparison with the predictions of some theoretical models and some available IR data is made.

High-resolution infrared difference frequency laser spectroscopic characterization of methane discharge plasmas

Using an original double modulation set-up of an IR difference frequency laser spectrometer and a hollow cathode discharge cell with methane, in addition to a double phase sensitive detection method, it has been possible to distinguish between (nu) 3 band spectral lines of the CH3 radical and the much stronger lines belonging to the C-H stretching bands of the precursor and other stable species (C2H4, C2H6) that appear in the discharge. The method has proved to be very sensitive to detect population variations versus temperature of very weak transitions from highly excited levels of CH4 and other stable species. The temperature characterization of several neutral species involved in the hollow cathode discharge has been tested and remarkably low temperatures have been obtained.

High-resolution stimulated Raman spectroscopy of ethane

ABSTRACT High resolution stimulated Raman spectra of the Q branches in the regions of the v and v3 Raman active modes of ethane (12C2H6) have been recorded. A complete analysis of the v3 region in terms of a vibrational torsional coupling has been achieved. For the v region spectra at 300 K, 173 K (static) and 30 K (jet expansion) have been recorded. On the basis of the 30 K spectrum, a preliminar assignment of the stronglyperturbed spectra is presented. INTRODUCTION Ethane can be considered as one of the prototype molecules with periodic torsional potentials. Several highresolution infrared bands of ethanet5 have been analyzed by taking into account perturbative effects on the rovibrational levels due to the torsional motion6. To our knowledge just one high resolution (stimulated) Ramanspectrum of ethane around 2950 cm1 has been previously reported7. So far no assignment has been proposed for this spectrum. We have investigated the high resolution stimulated Raman spectra of ethane in the v and

INFRARED DIFFERENCE FREQUENCY LASER AND SRS SPECTROMETERS. Q–BRANCH OF CD3H ν1 BAND

Publisher Summary This chapter discusses the recording of Stimulated Raman and infrared (IR) spectra using infrared difference frequency laser and stimulated-Raman-scattering spectrometers. The chapter presents an experiment in which a cw difference frequency IR laser spectrometer was used that was constructed following the design of Pine. The output of a frequency stabilized Ar+ laser and that of a commercial ring dye laser were mixed collinearly and focused into a 5 cm long, a-cut, lithium niobate crystal, held in a temperature-controlled oven to achieve phase matching. The generated IR radiation was recollimated to allow long absorption paths. Two indium antimonide detectors were used in a dual-beam configuration to obtain transmittance spectrum. Amplitude modulation and lock-in detection were then used. Data was acquired, stored, and processed with an AT-compatible computer. The whole experimental arrangement was schematically depicted. The setup allowed consecutive recording of Stimulated Raman and IR spectra just by the insertion of a couple of mirrors.