Measurements of air and noble-gas broadening and shift coefficients of the methane R3 triplet of the 2ν3 band

Zéninari, V.; Parvitte, B.; Courtois, D.; Kapitanov, V. A.; Ponomarev, Yu. N.

doi:10.1007/s003400100586

Cited by 27 publications

(15 citation statements)

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“…Different buffer gases (N 2 /O 2 mixtures of different compositions, adjunction of several percent of water vapour or helium) have been used in our experiments in order to study the influence of molecular relaxation on the PA signal. Since the foreign-broadening coefficient of the CH 4 absorption feature of interest changes with the composition of the carrier gas [23], IM has been preferred since it is less dependent on the width of the absorption feature than WM. For this purpose, the laser current was square modulated between threshold and a value close to the current limit, in order to achieve complete IM (IM index M = 1).…”

Section: Methodsmentioning

confidence: 99%

Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation

2005

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A photoacoustic sensor has been developed for trace-gas monitoring using a near-infrared semiconductor laser emitting in the 2ν 3 band of methane at 1.65 µm. The apparatus was designed for on-line process control in the manufacturing of the novel low-water-peak fibres developed for optical telecommunications. The importance of collisional relaxation processes in the generation of the photoacoustic signal is reported in the particular case of CH 4 detection in dry O 2 and O 2 -N 2 mixtures. The negative influence of these effects results in a strongly reduced and phase-shifted photoacoustic signal, induced by a fast resonant coupling between the vibrational states of methane and oxygen, associated with the slow relaxation of the excited oxygen molecules. An unusual parabolic response of the sensor with respect to the methane concentration has been observed and is discussed. Finally, the beneficial effect of several species, including water vapour and helium, acting as a catalyst to hasten the relaxation of the CH 4 -O 2 system, is demonstrated.PACS 42.62.Fi; 33.20.Ea; 34.50.Ez IntroductionInfrared photoacoustic spectroscopy (PAS) is widely recognized for its high performances in trace-gas monitoring and is one of the most sensitive techniques to measure low gas concentrations at atmospheric pressure [1]. The high sensitivity of PAS mainly results from its zero-background nature, which means that no signal is produced in the absence of an absorbing species. Furthermore, one of the most outstanding features of this technique is its achromaticity: the response of a photoacoustic (PA) sensor, represented by the cell constant (i.e. the PA signal normalized by the laser power and absorption coefficient), is usually independent of the laser excitation wavelength (however, a few exceptions may occur in some particular situations, as will be discussed later). It means that the same PA detector can be used with any type of laser and at any wavelength, from ultraviolet to mid infrared (MIR), with identical performances in terms of cell constant (provided that a suitable window material is used in the PA cell). This is definitively not the case for other high u Fax: +41-21-693-26-14, E-mail: stephane.schilt@epfl.ch sensitivity laser spectroscopy techniques, such as wavelengthor frequency-modulation spectroscopy (WMS/FMS), cavity ring-down spectroscopy (CRDS) or intracavity laser absorption spectroscopy (ICLAS), which all make use of optical detection that has poorer performances in the MIR region. Indeed, not only is the sensitivity of MIR photodiodes strongly reduced in comparison to near-infrared (NIR) ones, but also MIR detectors require low-temperature operation and are much more expensive than NIR detectors.For several years, there has been much interest in the use of NIR semiconductor lasers in PAS, such as distributedfeedback (DFB) lasers mass produced for the optical telecommunications market, whereas, primarily, it has been predominantly implemented using MIR gas lasers (CO or CO 2 lasers). Extreme detectio...

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Section: Methodsmentioning

confidence: 99%

Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation

2005

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“…[22]). The overview of recent 2ν 3 Table 1 illustrates the broad range of measurements [23][24][25][26][27][28][29][30][31][32] to improve the quality and quantity of such parameters by using different line shapes. Further research is required to meet the needs for the state-of-the-art remote sensing.…”

Section: Introductionmentioning

confidence: 99%

Self- and air-broadened line shapes in the 2ν3 P and R branches of 12CH4

Devi

Benner

Sung

et al. 2015

Journal of Molecular Spectroscopy

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“…These same authors later published room temperature measurements for 740 transitions, as well as the temperature-dependence coefficients for airbroadened widths and shifts of 370 lines in the same spectral region [4]. These coefficients were determined by analyzing one spectrum at a time and combining the retrieved values; this was the case for most of the past studies of air-broadened methane [5][6][7][8][9][10]; a notable exception is the work of Pine and Gabard [9] who applied the multispectrum measurement technique in a study of speed dependence line shapes with line mixing for the allowed transitions in m 3 .…”

Section: Introductionmentioning

confidence: 99%

“…These accurate air-broadening and air-shift coefficients will support tropospheric remote sensing and guide the development of better theoretical models for widths and shifts of methane transitions. Air-broadening measurements of infrared methane bands available in the literature [3][4][5][6][7][8][9][10] also permit investigations of the vibrational and rotational dependences of the broadening coefficients.…”

Section: Introductionmentioning

confidence: 99%

Multispectrum analysis of 12CH4 from 4100 to 4635cm−1: II. Air-broadening coefficients (widths and shifts)

Predoi‐Cross

Brawley-Tremblay

Brown

et al. 2006

Journal of Molecular Spectroscopy

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Room temperature Lorentz air-broadened halfwidth and pressure-induced air-shift coefficients were measured for 1011 transitions in the octad region of methane between 4100 and 4635 cm À1 . These measurements were made by analyzing 10 laboratory absorption spectra recorded at 0.011 cm À1 resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 2.05 and 150 cm. The total sample pressures ranged from 99 to 400 torr with CH 4 volume mixing ratios of 0.01 in dry air. The spectral line parameters were retrieved using a multispectrum nonlinear least squares technique. Transitions belonging to five bands of the octad polyad were observed, namely m 2 + 2m 4 , m 1 + m 4 , m 3 + m 4 , 2m 2 + m 4 , and m 2 + m 3 . The numbers of measurements by bands are: 33 for m 2 + 2m 4 , 180 for m 1 + m 4 , 635 for m 3 + m 4 , 33 for 2m 2 + m 4 , and 130 for m 2 + m 3 . Transitions with rotational quantum number J up to 16 are included in the analysis. The measured width and shift coefficients vary according to the tetrahedral symmetry species and the rotational quantum numbers of the transitions. The retrieved parameters from this study are compared with prior results, in part to estimate absolute accuracy and determine the extent of vibrational dependence of widths and shifts.

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Measurements of air and noble-gas broadening and shift coefficients of the methane R3 triplet of the 2ν3 band

Cited by 27 publications

References 0 publications

Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation

Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation

Self- and air-broadened line shapes in the 2ν3 P and R branches of 12CH4

Multispectrum analysis of 12CH4 from 4100 to 4635cm−1: II. Air-broadening coefficients (widths and shifts)

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