High-resolution IR cavity ring-down spectroscopy of jet-cooled free radicals and other species

Abstract

Initial spectral results are reported from a newly constructed cavity ringdown spectrometer. The apparatus incorporates a slit-jet expansion, with or without a discharge, to produce cold sample molecules. High spectral resolution in both the near- and mid-IR is obtained by using stimulated Raman scattering of the pulsed amplified output of a cw Ti:Sa ring laser. Molecular spectra presented include the electronic near-IR transitions a (1)Delta(g)(-)<-- X (3)Sigma(g)(-) of O(2) and B (3)Pi(g)<-- A (3)Sigma(u)(+) of metastable N(2) and vibrational overtones of H(2)O (polyad 2) and the OH radical. Fundamental vibrational transitions of CH(3) (nu(3)) in the mid-IR are also observed. This apparatus has demonstrated the potential for obtaining high-resolution spectra of both reactive and non-reactive species throughout the entire IR region.

High-resolution cavity ringdown spectroscopy of the jet-cooled ethyl peroxy radical C2H5O2

“…Therefore, we decided to first investigate the G conformer 0 0 0 band with our high resolution jet-cooled appa- ratus, since the T conformer would have negligible population if the conformers were in equilibrium at the 15 K rotational temperature typical of the apparatus. 26 We were able to record the spectra of both the normal and deuterated species of the G conformer with a good signal to noise ratio ͑S / N Ϸ 60-100 for the strongest features͒. Figure 1, a scan over about 20 cm −1 of the two isotopologues, shows that the spectra are highly congested, primarily due to the population of many rotational and spin-rotational levels even at a temperature of Ϸ15 K. Because of this congestion, assignments of spectral features to individual transitions are mostly impossible.…”

“…We recently developed an experimental apparatus combining a high-resolution laser source 25 with a jet-cooled CRDS setup 26 and have applied 27 this apparatus to record the rotationally resolved à − X spectrum near 1.35 m of the perdeuterated methyl peroxy radical, CD 3 O 2 . The experimental spectrum has been modeled using a Hamiltonian that includes the rigid body rotation of an asymmetric top and the spin-rotation interaction.…”

Spectroscopic studies of the $\tilde{A}$Ö$\tilde{X}$X̃ electronic spectrum of the β-hydroxyethylperoxy radical: Structure and dynamics

“…[5][6][7][8] Details about the present experimental work not described in the previous papers will be described in this section.…”

“…4 Jet cooled high-resolution cavity ringdown spectroscopy (CRDS) studies on peroxy radicals [5][6][7] are useful for diagnostic purposes, experimentally characterizing the molecule, and benchmarking quantum chemical calculations. 8 The β-hydroxyethylperoxy (2-hydroxyethylperoxy) radical in the atmosphere arises from the reaction of ethene (CH 2 CH 2 ) and hydroxy radical (OH), followed by reaction with oxygen (O 2 ). 9 Ethene is an abundant organic compound in the troposphere with total annual emissions of between 18 and 45 Tg from both biogenic and anthropogenic sources.…”

Trace gas measurements using optically resonant cavities and quantum cascade lasers operating at room temperature

“…Early experiments in the latter region were carried out with optical parametric oscillators pumped with adequately powerful lasers, e.g., in 1995 by Scherer et al [19][20][21] The application of Raman cells or shifters was another method of choice in several studies of free radicals and stable species among them OH, CH 3 , or clusters of water and CH 3 I. [22][23][24][25][26] Peeters et al. 27 measured ethylene at 10 m with a waveguide CO 2 laser in a CEAS configuration.…”