Information theoretic investigation of vibrationally excited diatomic molecules in an inert matrix

Abstract

A surprisal analysis and synthesis of the vibrational population P v of CO molecules in an Ar matrix yields the following results: (1) The three dominant dynamical processes of the system, i.e. resonance and phonon assisted vibrational-vibrational energy transfer and fluorescence, may be expressed as constraints on the population of the molecules in the ground vibrational state and on the first two vibrational level moments of the distribution. The information of these constraints suffices to predict all P v′s. (2) Following the initial laser excitation, the dynamical processes maintain the CO vibrational manifold in an energy-rich state of considerable disequilibrium for a long time. As the matrix (and hence the final, equilibrium, vibrational state distribution, P v 0 ) is rather cold, the magnitude of the surprisal is dominated by the magnitude of P v 0. Using this result as well as the near-exponential decay of the first moment, we draw the following thermodynamic conclusions: (3) Almost the maximum available work of the vibration modes is really carried out, namely mainly as fluorescence and only marginally as heat added to the phonon bath. (4) The corresponding temperature increase of the matrix is less than 0.0 1 K. (5) Due to the phonon assisted vibrational up-pumping, the entropy of the vibrational distribution decreases. The anharmonic level scheme requires, however, that during the up-pumping energy is taken up by the matrix. The resulting entropy increase of the matrix is shown to compensate for the decrease in the entropy of the vibration leading to a net overall entropy increase, as expected.