Helium-broadened line shapes of the rovibrational transitions of the (ν1 + 3ν3) combination-overtone band of C2H2 have been studied by using a near IR diode laser spectrometer. The 2f frequency detection technique has been employed for signal detection of these weak band transitions. The linestrength parameters and broadening coefficients (HWHM) have been extracted by fitting the observed line shapes with Voigt profiles. Helium, lightest noble gas perturber, exhibits the effect of close collisional dephasing on pressure broadened line profiles. Due to overlapping of atomic orbitals the repulsive interaction dominates over attractive interaction for collision diameter in the 3 to 4 Å range. In order to interpret this type of linear polyatomic-monatomic collision phenomena the Tipping-Herman potential has been chosen. Emphasis has been given to the analysis of observed data to obtain information about interaction potential, phase-shift and molecular constants. The results obtained from detailed semi-classical model calculations are found to be in good agreement with the observed data.

BISWAJIT RAY

Physics

B K DUTTA

D BISWAS

P N GHOSH

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

European Physical Journal D

A near infrared diode laser spectrometer has been used for measurement of line shapes of the rotational transitions of the (ν1 + 3ν3)overtone-combination band of acetylene perturbed by oxygen and air. Pressure-broadening coefficients and line strength parameters are extracted from least squares fitting of the spectra with Voigt profiles. A detailed calculation of pressure-broadening coefficients for the self, nitrogen and oxygen broadening cases has been performed by using semi-classical impact theory based on quadrupolar and dispersion interactions. The relative importance of the intermolecular interactions has been investigated and it is found that for these weak interaction cases dispersive terms have a dominant role in line broadening. This is more pronounced for the O2-broadening case. We have included all the non-resonant terms till convergence is achieved. The cutoff parameter b0 of the Anderson procedure has been determined separately for each non-resonant process. In order to include the orientation effect of the molecules at the moment of collision we have considered an average kinetic collision diameter which sets the lower limit of b0. This improves the result considerably and the calculated values are close to the observed results. The J-dependence of the half width is also reported and shows decrease for large J-values.

Diode laser spectroscopic measurement and impact theoretical analysis of collision broadening of acetylene (Î½1 + 3Î½3) band transitions

A near-infrared diode laser spectrometer is set up to study the absorption line shape of acetylene in the 782 nm region. The second-derivative spectra recorded by source modulation technique have enhanced sensitivity. Careful choice of operating current and diode temperature leads to distortion-free line shape for six rotational components of the (v1 + 3v3) overtone-combination mode of acetylene. Self- and nitrogen-broadening coefficients and line-strength parameters have been extracted by fitting the observed line shape with Voigt profiles. There is no evidence of the effect of velocity changing collisions on the line shape in this near-infrared band.

Applied Physics B: Lasers and Optics

Diode laser spectroscopic measurement of line shape of (v1 + 3v3) band transitions of acetylene

Helium broadening of the oxygen atmospheric A-band rovibrational transitions in the 759 nm region has been measured using a diode laser spectrometer. He-broadening coefficients are found to be smaller than the self-broadening coefficients. Non-linear least-squares fitting of the observed spectra by Voigt and Galatry profiles show little effect of narrowing on the spectral lineshape. © 1997 Published by Elsevier Science B.V.

Chemical Physics Letters

He-broadening of the O2 A-band transitions studied by diode laser spectroscopy

Measurement of pressure-dependent half-width of the rovibronic transitions of the oxygen A-band shows that the width remains almost unchanged at low pressure. Simulations based on soft collision model reveal that the collisional narrowing of the Doppler component compensates the pressure broadening up to a pressure of nearly 100 T. At higher pressure the line shape is non-Voigt type and has reduced but constant Doppler broadening. © 1997 Elsevier Science B.V.

Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

Collisional narrowing and pressure broadening of the oxygen A-band transitions

Journal of Chemical Technology & Biotechnology

CRC Handbook of Chemistry and Physics-69th Edition Editor in Chief R. C. Weast, CRC Press Inc., Boca Raton, Florida, 1988, pp. 2400, price £57.50. ISBN 0-8493-0369-5

Journal	European Physical Journal D
Publisher	-
ISSN	1434-6060