Because photochemical hole burning (PHB)

population hole burning and photon echo are all performed on zero-phonon line (ZPL)

it is useful to study ZPL and vibrational mode.We have obtained the absorption spectrum of tetraphenyporphin (TPP) in cellulose acetate film at room temperature which contains four bands peaking at 649

594

552 and 516 nm respectively. They originated from the absorption transition of TPP

while host cellulose acetate does not contribute to this range of the absorption spectrum. The band centered at 649 nm is ZPL of TPP (0-0 transition) and its FWHM is about 2Cnm.By fitting the experiment data of the ZPL with Lorentzian and Gaussian line shapes respectively

it is shown that the ZPL is close to Gaussian. The ZPL is inhomogeneousely broadened.