Rotational dephasing of symmetric top molecules: Analytic expressions and applications

An analytic expression for the rotational dephasing of an ensemble of symmetric top molecules excited by a short laser pulse is developed. This expression can be used to discern rotation from electronic and vibrational dynamics in polarization resolved studies and is computationally less demanding than numeric simulations used previously. The result agrees well with quantum mechanical treatment, both at room temperature and at cold rotational temperatures found in molecular beams. Applications to transient anisotropy and photoelectron angular distributions are given. Finally, we raise the possibility of combining transient anisotropy techniques with time-resolved photoelectron spectroscopy.