title: Vibrational energy relaxation of the ND-stretching vibration of NH2D in liquid NH3.
abstract: 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.
authors: Institut für Physikalische Chemie, Universität Göttingen, Göttingen, Germany.
authors: Tim
authors: T
authors: Schäfer
authors: Alexander
authors: A
authors: Kandratsenka
authors: Peter
authors: P
authors: Vöhringer
authors: Jörg
authors: J
authors: Schroeder
authors: Dirk
authors: D
authors: Schwarzer
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry; D004735:Energy Transfer; D056004:Molecular Dynamics Simulation; D009584:Nitrogen / Q000737:chemistry; D011789:Quantum Theory; D014732:Vibration
chemical_list: D000641:Ammonia; D003903:Deuterium; D009584:Nitrogen