Spectral Calculator-Hi-resolution gas spectra

Continuum absorption/emission effects for N2, O2 and H2O are modeled using the approaches described by Clough, et al. [1] and Lafferty et al. [2]. These continuum models augment the standard "line-by-line" calculation, more accurately accounting for far-wing effects at high pressures.

For O2 and N2, the spectral ranges affected are 1345-1820 cm^-1 and 2105-2620 cm^-1 respectively. The H2O continuum is significant at wavenumbers below 600 cm^-1 and between 1200 and 2000 cm^-1.

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Gas cell simulations of N2, O2 and H2O spectra in any of the above wavebands will automatically include the appropriate continuum model(s). No action is needed from the user.

For all three gases, the effect is proportional to pressure, and is negligible at pressures less than ~10mbar. Temperature dependence of the continua is included in the model, derived from laboratory measurements between 70 and 350 K. Continuum absorption for spectra at higher temperatures is based on extrapolation of these data, and therefore may contain some inaccuracies. Note, however that the continuum effects are inversely proportional to temperature, so the overall magnitude become negligible for high temperatures.

[1] Clough, S. A., F. X. Kneizys, and R. W. Davies, "Lineshape and the water vapor continuum," Atmos. Res. 23, 229-241 (1989)

[2] Lafferty, W. J., A. M. Solodov, A. Weber, W. B. Olson, and J. Hartmann, "Infrared collision-induced absorption by N2 near 4.3 µm for atmospheric applications: measurements and empirical modeling," Appl. Opt. 35, 5911-5917 (1996)