Vibrational dynamics of pyrrole via frequency-domain spectroscopy

The N-H stretch overtones of pyrrole, a key constituent of biologic building blocks, were studied by room temperature photoacoustic and jet-cooled action spectroscopies to unravel their intramolecular dynamics. Contrary to isolated states excited with two and three N-H stretch quanta, the one with four quanta shows strong accidental resonances with two other states involving three quanta of N-H stretch and one quantum of C-H stretch. The inhomogeneously reduced features in the action spectra provide the means for getting insight into the intramolecular interactions and the factors controlling energy flow within pyrrole. The time dependence of the survival probability of the 4 ₁ N-H stretch, deduced from the vibrational Hamiltonian, shows an initial decay in ∼0.3 ps with ensuing quantum beats from the N-H - C-H resonance and their decay with a time constant of about 5 ps as a result of weaker coupling to bath states.