H2-broadening in the ν7 band of ethylene by diode-laser spectroscopy

Using a tunable diode-laser spectrometer, we have measured H-2-broadening coefficients for 34 lines of C2H4 in the v(7) fundamental band. The studied transitions J', K-a', K-c' <-- J", K-a", K-c" with J" ranging from 2 to 23, K-a" from 0 to 4, and K-c". from 2 to 22 in the P, Q, and R branches are located in the spectral range 919-1023 cm(-1). The collisional widths are obtained by modeling each spectral line with a Voigt and a Rautian profile. The measured broadening coefficients belonging to transitions with the same J" generally increase with increasing K-a" and these coefficients decrease slightly on the whole with increasing J". These behaviors can be roughly predicted by an approximate semiclassical calculation performed by using in addition to the weak electrostatic contributions a simple formalism for the contribution of the intermolecular potential. (C) 2003 Published by Elsevier Science (USA).