* Corresponding author. Fax: #1-256-851-5622. E-mail address: aamaxs01@aamu.edu (A. Sharma). Journal of Quantitative Spectroscopy & Radiative Transfer 69 (2001) 151}158 Pressure-induced self-broadening and frequency shift measurements of absorption lines of acetylene using tunable diode laser absorption spectroscopy C. Yelleswarapu, A. Sharma* Department of Physics, Alabama A&M University, Normal, AL 35762, USA Received 16 April 2000 Abstract Diode laser spectroscopy is used to investigate pressure-induced self-broadening as well as frequency shifts of several absorption lines in the   #3  overtone band around 780 nm region. A 35 meter path-length multipass cell is used to measure absorption directly as well as with the wavelength}modulation technique involving detection at "rst and second harmonics of the modulation frequency. Acetylene pressures in the 5}600 Torr range are used. Absorption linewidths are measured with Fabry}Perot interferometer having a free spectral range of 750 MHz. Frequency shift measurements and pressure-broadening coe$cients of some spectral lines are reported for the "rst time.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Wavelength modulation; Pressure induced broadening 1. Introduction The recent advances in tunable semiconductor diode lasers have been of great importance for an increasing number of applications in both pure and applied spectroscopy. One of the important applications is monitoring the environment. Acetylene (C  H  ) is one of the trace constituents of the earth's atmosphere, mainly produced by anthropogenic sources [1}5]. It has been suggested that this molecule might play a non-negligible role in the global climate of this planet, due to the increasing use of automobiles [6]. In the atmosphere, C  H  is essentially destroyed by chemical reaction with OH and Cl, and its detection may help us to better understand the ozone cycles [1]. Traces of C  H  were detected in the arctic hazes, contributing to the development of pollutants transport models [3]. 0022-4073/01/$ - see front matter  2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 2 - 4 0 7 3 ( 0 0 ) 0 0 0 7 3 - X