In this paper, we study the temperature effect and effect of the inter
action between the adsorbed molecule and heat bath on the band-shape f
unction of IR-UV sum frequency generation (SFG). Numerical calculation
s have been performed to demonstrate these effects. We have also compa
red the IR-visible SFG and FT-IR spectroscopy and considered the effec
ts of inhomogeneities on the SFG and IR spectra.