Low temperature cell for cavity ring down absorption studies

Abstract

A rigid, monolithic but still scannable cavity ring-down spectroscopy cell Rev. Sci. Instrum. 83, 043115 (2012); 10.1063/1.3700978Ab initio calculations of low-lying electronic states of vinyl chloride Phase shift cavity ring down is a technique that due to its long optical path length is an ideal method to detect weak absorptions. Coupling the method to a custom fitted cryostat allows gas phase molecules to be studied at cryogenic temperatures in a thermally isolated vacuum chamber. A novel design is described to construct the complete instrument. With optical cavities of length 10ഛ ᐉ ഛ 43 cm, optical path lengths between 200 m and 6 km have been achieved. High vibrational overtones C-H ͑⌬ =5͒ are measured at 130 K ͑methane͒, 150 K ͑ethylene͒, and 155 K ͑ethane͒. Oscillator strengths of each molecule calculated at different temperatures are in excellent agreement. The experimental setup can be used to study kinetics and spectroscopy of atmospheric molecules, planetary atmospheres, and molecular complexes in the gas phase. Low temperatures can be obtained using liquid He or liquid N 2 as cryogens.

Vibrational Overtone Spectroscopy, Energy Levels, and Intensities of (CH3)3C—C≡C—H

“…The advantage of the phase shift technique is that no signal averaging is necessary and the spectra can be obtained in a very short time. We have shown 12 that if the laser bandwidth is smaller than the absorption band, the measured cross sections are as good as the ones obtained with conventional absorption techniques. In this investigation the absorption bands are obtained at different pressures and the integrated bands are plotted versus the density of the gas sample to obtain the experimental cross section to be compared with theoretical calculations.…”

Phase shift cavity ring down and Fourier transform infrared measurements of C–H vibrational transitions, energy levels, and intensities of (CH3)3Si–C≡C–H

“…The spectra were taken at 295 K. The experimental set up for the PS-CRD technique has been given in previous publications. 16,17 In this technique two different lasers are used in the range between 12 200 and 14 300 cm −1 (Ti:sapphire) or in the range from 14 800 to 16 700 cm −1 (dye laser). The modulated excitation laser beam passes through the optical cavity and is detected with a photomultiplier.…”

Low temperature cavity ring down spectroscopy with off-axis alignment: application to the A- and γ-bands of O2 in the visible at 90 K

“…Experimental details of our technique, cryostat, and low temperature optical cavity have been given in previous publications [1][2][3]. Figure 1 (top) summarizes the main components of the low temperature optical cavity.…”

“…With our experimental set up, CRD is performed with a variable temperature (77-297 K) cavity [3,4]. Our cavity design is such that the complete optical cavity including the mirrors is in a vacuum chamber at the temperature of the cold head of the cryostat.…”