Vibrational energy relaxation of the ND-stretching vibration of NH2D in liquid NH3.

Tim Schäfer, Alexander Kandratsenka, Peter Vöhringer, Jörg Schroeder, Dirk Schwarzer

Institut für Physikalische Chemie, Universität Göttingen, Göttingen, Germany.

Physical chemistry chemical physics : PCCP 2012 Sep 7

filter terms:

The vibrational energy relaxation from the first excited ND-stretching mode of NH(2)D dissolved in liquid NH(3) is studied using molecular dynamics simulations. The rate constants for inter- and intramolecular energy transfer are calculated in the framework of the quantum-classical Landau-Teller theory. At 273 K and an ammonia density of 0.642 g cm(-3) the calculated ND-stretch lifetime of τ = 9.1 ps is in good agreement with the experimental value of 8.6 ps. The main relaxation channel accounting for 52% of the energy transfer involves an intramolecular transition to the first excited state of the umbrella mode. The energy difference between both states is taken up by the near-resonant bending vibrations of the solvent. Less important for the ND-stretch lifetime are both the direct transition to the ground state and intramolecular relaxation via the NH(2)D bending modes contributing 23% each. Our calculations imply that the experimentally observed weak density dependence of τ is caused by detuning the resonance between the ND-stretch-umbrella energy gap and the solvent accepting modes which counteracts the expected linear increase of the relaxation rate with density.

Citation

Tim Schäfer, Alexander Kandratsenka, Peter Vöhringer, Jörg Schroeder, Dirk Schwarzer. Vibrational energy relaxation of the ND-stretching vibration of NH2D in liquid NH3. Physical chemistry chemical physics : PCCP. 2012 Sep 7;14(33):11651-6