Band-integrated infrared absorptance of low-molecular-weight paraffin hydrocarbons at high temperatures

The spectral absorptance of the 3.4-mu m band of methane, ethane, propane, and butane has been measured with a Fourier transform infrared spectrometer over a range of temperatures from 296 to 900 K. The measurements were made at a 4-cm(-1) resolution and integrated over the entire band to give the t otal absorptance. The total absorptance is found to behave in such a way th at it can be correlated by a combination of algebraic expressions that depe nd on the gas temperature and concentration. Average discrepancies between the correlations and the measurements are less than 4%, with maximum differ ences of no greater than 17%. In addition, the correlations presented here for methane are shown to be in good agreement with established models. Expr essions given for the integrated intensity of each gas show an inverse depe ndence on temperature, reflecting the associated change in density. (C) 199 9 Optical Society of America OCIS codes: 300.0300, 300.1030, 800.6300, 300. 6340, 300.6390.