High resolution stimulated Raman spectroscopy from collisionally populated states after optical pumping: the 3ν₂←2ν₂and ν₂+2ν₄+ν₅←2ν₄+ν₅ Qbranches of¹²C₂H₂and the 3ν₂←2ν₂ Qbranch of¹²C₂D₂.

Abstract

In this work, we demonstrate the combined use of a pump‐probe Raman–Raman technique and the naturally occurring process of vibration‐to‐vibration (V–V) collisional relaxation to populate and obtain high‐resolution Raman spectra of vibrationally excited states that cannot be easily accessed by other means. First, a stimulated Raman pump stage is used to promote population to a vi = 1 excited state. This is followed by a time interval whose length is chosen so that, at the working pressure, significant V–V collisional energy transfer takes place and the quanta of vibrational excitation initially placed in vi = 1 naturally reach other excited states. Finally, after this delay, the probe stage is used to obtain high‐resolution Raman spectra of hot bands departing from these collisionally populated states. The technique has been demonstrated on two isotopologues of acetylene, 12C2H2 and 12C2D2, and has allowed the observation of transitions departing from the 2ν2 ( Σg+) and 2ν4 + ν5 (IΠu) collisionally populated states. Accurate values of the spectroscopic parameters for the v2 = 3 vibrationally excited states for both isotopologues were obtained, for the first time, from the least‐squares analysis of the assigned transitions. In addition, the observation of Q branch lines of v2 = 1, v4 = 2, v5 = 1 (IΠu) ← v4 = 2, v5 = 1 (IΠu) band for 12C2H2 allowed the spectroscopic characterization of the upper state. Copyright © 2016 John Wiley & Sons, Ltd.

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…They used a pump‐probe Raman‐Raman technique, and the naturally occurring process of vibration‐to‐vibration collisional relaxation to populate to obtain high‐resolution Raman spectra of vibrationally excited states that cannot be easily accessed by other means . In a closely‐related paper first published, these same authors reported high resolution SRS from collisionally populated states after optical pumping: the 3ν2←2ν2 and ν2+2ν4+ν5←2ν4+ν5 Q branches of 12 C 2 H 2 and the 3ν2←2ν2 Q branch of 12 C 2 D 2 …”

Frequency comb assisted two-photon vibrational spectroscopy

“…Spectroscopy methods based on stimulated two-photon transitions, such as two-photon absorption, stimulated emission probing, and stimulated Raman spectroscopy, allow accessing energy states in which typical single photon excitations are forbidden under spectroscopic selection rules [1][2][3]. Stimulated two-photon transition can be used to measure spectral features at sub-Doppler resolution, without the need for cooling or molecular jets [4].…”

High‐resolution stimulated Raman spectroscopy from collisionally populated states after optical pumping (II): 13C2H2, 13C12CH2, 13C12CD2 and 13C2D2

“…The first results of this study, concerning 12 C 2 H 2 and 12 C 2 D 2 , have already been published. [1] This article presents the results obtained for four other isotopologues: 13 C 2 H 2 , 13 C 12 CH 2 , 13 C 12 CD 2 and 13 C 2 D 2 . The goal of the study is to spectroscopically observe and characterize vibrationally excited states from levels not significantly populated at room temperature and thus difficult to observe by normal means.…”

“…A detailed discussion of the vibration-tovibration collisional energy transfer processes, including an energy diagram representing the vibrationally excited states more likely to be populated by these processes in the molecule of acetylene, can be found in reference. [1] The ν 2 vibration has been selected for both optical pumping and spectroscopy due to its large Raman scattering cross section. Thus, population pumping will take place through the v 2 = 1 ← v 2 = 0 transition, and the spectroscopy stage will probe for transitions that involve a change of one quantum of ν 2 .…”

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The combined use of a pump-probe Raman-Raman technique and the naturally occurring process of vibration-to-vibration collisional relaxation to populate and obtain high-resolution Raman spectra of vibrationally excited states that cannot be easily accessed by other means has been recently demonstrated in 12 C 2 H 2 and 12 C 2 D 2 (Martínez et al). [1] This technique has been here applied to four other isotopologues of acetylene, namely 13 C 2 H 2 , 13 C 12 CH 2 , 13 C 12 CD 2 and 13 C 2 D 2 . Transitions from the v 2 = 2 and v 4 = 2, v 5 = 1 collisionally populated states have been observed.

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