Application of the Hartmann–Tran profile to precise experimental data sets of 12C2H2

Abstract

Self- and nitrogen-broadened line shape data for the Pe(11) line of the ν1+ν3 band of acetylene, recorded using a frequency comb-stabilized laser spectrometer, have been analyzed using the Hartmann–Tran profile (HTP) line shape model in a multispectrum fitting. In total, the data included measurements recorded at temperatures between 125K and 296K and at pressures between 4 and 760Torr. New, sub-Doppler, frequency comb-referenced measurements of the positions of multiple underlying hot band lines have also been made. These underlying lines significantly affect the Pe(11) line profile at temperatures above 240K and poorly known frequencies previously introduced errors into the line shape analyses. The behavior of the HTP model was compared to the quadratic speed dependent Voigt profile (QSDVP) expressed in the frequency and time domains. A parameter uncertainty analysis was carried out using a Monte Carlo method based on the estimated pressure, transmittance and frequency measurement errors. From the analyses, the Pe(11) line strength was estimated to be 1.2014(50)×10−20 in cmmolecule−1 units at 296K with the standard deviation in parenthesis. For analyzing these data, we found that a reduced form of the HTP, equivalent to the QSDVP, was most appropriate because the additional parameters included in the full HTP were not well determined. As a supplement to this work, expressions for analytic derivatives and a lineshape fitting code written in Matlab for the HTP are available.