  Interaction of molecules with light may lead to electronic transitions and
simultaneous vibrational excitations. Franck-Condon factors (FCFs) play an
important role in quantifying the intensities of such vibronic transitions
occurring during molecular photo-excitations. In this article, we describe a
general method for estimating FCFs using a quantum information processor. The
method involves the application of a translation operator followed by the
measurement of certain projections. We also illustrate the method by
experimentally estimating FCFs with the help of a three-qubit NMR quantum
information processor. We describe two methods for the measurement of
projections - (i) using diagonal tomography and (ii) using Moussa protocol. The
experimental results agree fairly well with the theory.
