# When simulating spectral line broadening, which convolution is preferred?

Many computational chemistry packages permit the calculation of vibrational and electronic spectra. These spectra are obtained as a set of discrete eigenvalues however they are often convolved with some distribution to give a continuous spectrum that is realistic for a finite temperature, rather than a sequence of impulse functions.

The ADF package allows the user to convolve the spectrum with either a Gaussian or Cauchy (Lorentzian) function. My understanding is that the latter affords a more realistic line broadening, however the Gaussian must be there for a reason.

Which spectral broadening scheme is preferred? Why the choice?

• As I recall, it depends on the conditions the gas is under, if collisions are causing changes in the spectra or not. I can't remember which was which though. May 10 '12 at 4:41
• What are the 'raw' signals the vibrational and electronic spectra are calculated from? Do you first have some time-domain signals that are then transformed as frequency-domain signals?
– mmh
May 27 '15 at 15:21