Issue 33, 2012

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 NH2D dissolved in liquid NH3 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 NH2D 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.

Graphical abstract: Vibrational energy relaxation of the ND-stretching vibration of NH2D in liquid NH3

Article information

Article type
Paper
Submitted
30 Apr 2012
Accepted
03 Jul 2012
First published
23 Jul 2012

Phys. Chem. Chem. Phys., 2012,14, 11651-11656

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

T. Schäfer, A. Kandratsenka, P. Vöhringer, J. Schroeder and D. Schwarzer, Phys. Chem. Chem. Phys., 2012, 14, 11651 DOI: 10.1039/C2CP41382E

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