Pure intermolecular vibrational relaxation of the OH bending mode of water molecules

The Ehrenfest method with quantum corrections is used to describe the vibrational relaxation of the bend fundamental in liquid water. All the vibrational degrees of freedom of the water molecules are described using quantum mechanics, while the remaining translational and rotational degrees of freedom are described classically. The relaxation time obtained compares well with experiment and with relaxation times calculated using other theoretical approximations. The presence of resonant intermolecular vibrational energy (VV) transfer is established with a maximum percentage of excited molecules, different from the initial one, of 9.2%. It is found through an effective kinetic fit that two VV transfers occur before relaxation of water to the vibrational ground state.

Section: Introductionmentioning

confidence: 54%

Hybrid quantum/classical simulation of the vibrational relaxation of the bend fundamental in liquid water

Bastida

Zúñiga

Requena

et al. 2009

“…In fact, the 2 bending mode is involved in the relaxation of O-H stretch quanta of H 2 O in the condensed phase. [41][42][43][44] Another critical aspect affecting the 1 lifetime may be the fact that, according to the 2D PES, this energy level occurs only 42 cm Ϫ1 above the dissociation limit. Although current views of the VP process predict fast dissociation for low kinetic energy release, 12,13 the details of the VP process may depend sensitively on its exact value.…”

Section: Comparison To Experimentsmentioning

confidence: 99%

Infrared spectrum and predissociation dynamics of H2O+–Ar

Dopfer

Engel

2004

The infrared (IR) spectrum and vibrational predissociation of the proton-bound H(2)O(+)-Ar ionic complex are investigated within an ab initio and quantum dynamical study. For this purpose, a two-dimensional potential energy surface (2D PES) is determined as a function of the HO-H and OH-Ar coordinates. This PES is then employed in a wave-packet calculation to determine spectral properties of the system and to calculate the IR absorption spectrum. The vibrational energy levels and relative IR intensities agree well with the experimental spectrum reported earlier. On the other hand, the predissociation lifetimes in the nanosecond regime derived from the 2D PES are in disagreement with the experimental observations, indicating the importance of the neglected degrees of freedom for a correct description of the dynamics of the complex.

“…11 It is still unclear whether the stretch relaxation involves energy transfer to the bending mode, as in bulk water, [47][48][49] or to vibrational states of the solvent, as has been shown for the bending mode of monomeric water. 50 The substantially smaller detuning of the bend overtone from the stretching modes for H 2 O as compared to HDO ͑ϳ350 vs ϳ700 cm −1 , respectively͒ points toward the former scenario. Regardless of the precise relaxation pathways, the somewhat shorter lifetime found in the case of H 2 O can be qualitatively explained by the broader absorption line, which improves the resonance with the accepting mode͑s͒.…”

Section: -3mentioning

confidence: 99%

Ultrafast anisotropy dynamics of water molecules dissolved in acetonitrile

Cringus

Jansen

Pshenichnikov

et al. 2007

Infrared pump-probe experiments are performed on isolated H 2 O molecules diluted in acetonitrile in the spectral region of the OH stretching vibration. The large separation between water molecules excludes intermolecular interactions, while acetonitrile as a solvent provides substantial hydrogen bonding. Intramolecular coupling between symmetric and asymmetric modes results in the anisotropy decay to the frequency-dependent values of ϳ0 -0.2 with a 0.2 ps time constant. The experimental data are consistent with a theoretical model that includes intramolecular coupling, anharmonicity, and environmental fluctuations. Our results demonstrate that intramolecular processes are essential for the H 2 O stretching mode relaxation and therefore can compete with the intermolecular energy transfer in bulk water.