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Intensity of the Simultancous Vibrational Absorption CO2 (v3=1) + N2 (v=1) 2 (v3=0) + N2 (v=0) at 4680 cm-1

Published

Author(s)

B Mate, Gerald T. Fraser, Walter J. Lafferty

Abstract

Simultaneous or double vibrational collision-induced absorptions in compressed gas mixtures were extensively studied 30-40 years ago. Due to both their large linewidths and their overlap or near overlap with monomer absorptions, the intensities of these bands are difficult to measure accurately. None theless, frequencies and intensities of these transtions have been reported (1). In particular, the CO2-N2 simultaneous transitions have been reported (I). In particular, the CO2-N2 simultaneous transition, CO23 = 1) + N2 (υ = 1) 2 (υ = O), at 4680 cm-1 was first measured by Fahrenfort and Ketelaar (2) in the mid-1950s and, as far as we know, no other intensity studies have been made for this transition. Lineshape studies on this absorption, however, were later carried out by Brodbeck and Bouanich (3). At pressures from 4900 to 17 8000 kPa and path length of 2.26 m. In this work the intensity of the CO2 + N2 simultaneous absorption at 4680 cm-1 has been measured using a Bomem DA3.002 Fourier transform infrared spectrometer coupled to a long-path White-type cell that provides an 84.05-m optical path length (4). All the spectra were recorded at 1 cm-1 resolution using an InSb detector, a CaF2 beam splitter, and a Quartz blackbody source. The measurements were made at room temperature using CO2/N2 mixtures, with a partial density of CO2 between 2 and 5 amagats and a maximum total density of the mixture of 10 amagats. The amagat is the ratio of the density of the gas mixture at the pressure, P, and temperature, T, of the measurement to that at STP, where T = 273.15 K and P = 101.325 kPa. At each sample pressure two spectra consisting of 200 scans were taken and averaged. The sample pressure was determined to 0.1% accuracy using a capacitance manometer. The simultaneous transition band at 4680 cm1 overlaps with the weak 2υ318OCO and the 2υ1 + {upsion}313CO2 bands and, in the high frequency wing, with the strong 2υ1 + υ3 band of CO2 centered at 4860 cm-1. A simple subtraction of the CO2 spectrum from the CO2/N2 mixture spectrum will leave significant residuals due to the CO2 pressure broadening in the presence of N2. To avoid this problem, spectra of mixtures of CO2 and Ar were also taken. Assuming that Ar and N2 have nearly the same pressure-broadening coefficients. Different by only 15% (5), the CO2/AR spectrum has been subtracted from the CO2/N2 spectrum to obtain the simultaneous absorption spectrum. Nitrogen has no observable absorption features in the spectral region studied under our experimental conditions. Several higher resolution spectra (0.3 cm-1) were also taken, but no narrow structure was observed in this band, as observed previously in N2 and O2 collision-induced absorption bands (6, 7). An example of a CO2/N2 spectrum, a CO2/Ar spectrum, and the simultaneous transition spectrum obtained from the previous two is presented in Fig. 1 Several experimental simultaneous absorption spectra are presented in Fib 2. A nonlinear baseline correction was used to determine the integrated bandstrength. The baseline choice was based on the low frequency wing of the band.
Citation
Journal of Molecular Spectroscopy
Volume
201
Issue
No. 1

Keywords

carbon dioxide, collision-induced absorption, pressure broadening, simultaneous absorption

Citation

Mate, B. , Fraser, G. and Lafferty, W. (2000), Intensity of the Simultancous Vibrational Absorption CO<sub>2</sub> (v<sub>3</sub>=1) + N<sub>2</sub> (v=1) < CO<sub>2</sub> (v<sub>3</sub>=0) + N<sub>2</sub> (v=0) at 4680 cm<sup>-1</sup>, Journal of Molecular Spectroscopy (Accessed April 18, 2024)
Created May 1, 2000, Updated February 17, 2017