On the infrared fluorescence of monolayer 13CO:NaCl(100)

Computations are presented to describe and analyze the high levels of infrared laser induced vibrational excitation of a monolayer of absorbed (13)CO on a NaCl(100) surface. Extending the vibrational site-to-site surface hopping technique of Corcelli and Tully, kinetic Monte Carlo computations are used to incorporate single-quantum vibrational pooling and depooling of the (13)CO by phonon excitation to allow up to the n = 45 vibrational state under different lasing conditions. Previously unpredicted pooling peaks at n > 16 are calculated and, under the highest fluence conditions, pooling up to the n = 32 state is found in the calculation. These results lead to the prediction of a secondary local maximum in the dispersed fluorescence of monolayer CO:NaCl(100) under sufficiently high fluence excitation conditions. At times on the order of ms, we recover similar behavior for both high and low fluence results. The calculations confirm that, for situations where the Debye frequency limited n domain restriction approximately holds, the vibrational state population deviates from a Boltzmann population linearly in n, a result that we have derived earlier theoretically for a domain of n restricted to one-phonon transfers. This theoretically understood term, linear in n, dominates the Boltzmann term and is responsible for the inversion of the population of vibrational states, Pn.