Building transition probabilities for any condition using reduced cumulative energy transfer functions in H2O–H2O collisions (original) (raw)
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The mechanism of energy transfer in H2O–H2O collisions – a molecular dynamics simulation
Chemical Physics, 1998
Earlier work on the activation-deactivation mechanism of gas phase unimolecular reactions is extended to the study of the detailed energy transfer mechanism in collisions of water molecules. Molecular dynamics simulations of binary collisions between a reactant water molecule at high internal energy with medium molecules at various selected initial temperatures are Ž. Ž. compared with results from approximate statistical theory. Energy transfer is related to i interaction strength, ii hard Ž. Ž. Ž. atom-atom encounters, iii multiple minima in the center of mass separation, iv collision lifetime and v anharmonicity of the intramolecular potential function. The observed trends are interpreted within the framework of the partially ergodic Ž. multiple encounter theory PEMET of collisional energy transfer. By comparison with typical stable molecule collisions the water-water collisions are more efficient as a reflection of the strong hydrogen bonding interactions. A good agreement between PEMET and molecular dynamics simulations over a wide range of interaction strengths and initial reactant energies is shown, indicating the possibility of a priori use of the PEMET model.
Trajectory Calculations of Intermolecular Energy Transfer in H2O + Ar Collisions
Journal of Physical Chemistry A, 1999
The collisional energy transfer between excited SO2 and Ar has been simulated by classical trajectory calculations. The influences of the intramolecular and intermolecular potentials, of temperature, and of excitation of SO2 on vibrational and rotational energy transfer are demonstrated. Average energies transferred and collisional transition probabilities are reported. Permanent address: Australian Defence Force Academy, Canberra. measure this quantity. Instead, in general only first and second moments of k with respect to AE = E '-E are accessible ex-perime~~taIly.'-'~ With the assumption that total rate coefficients (1) Troe, J.
Progress on the modeling of the collisional energy transfer mechanism in unimolecular reactions
Berichte der Bunsengesellschaft für physikalische Chemie
Words: Computer Experiments / Elementary Reactions / Energy Transfer / Molecular Collisions Statistical Theory The RRKM theory of unimolecular reaction rates is a statistical mechanical theory based on an assumption of microcanonical equilibrium in the reactant phase space. The energy transfer in reactant medium collisions was originally described by a canonical strong collision assumption, i.e., an assumption of full thermal equilibration in each collision. In our work we first introduce a microcanonical strong collision assumption which gives the RRKM theory a consistent form. we then introduce parametrizations of the degree of weakness (nonergodicity) of the collisions. A concept of collision efficiency is defined. The weakness of the collision is expressed in terms of reduced subsets of active reactant and medium degrees of freedom. The corresponding partially ergodic collision theory (PECT) yields physical functional forms of the collisional energy transfer kernel P (E ' , E). In order to resolve the energy and temperature dependence and the dependence on interaction strength a multiple encounter theory is introduced (PEMET). Initially each encounter may be described by a semiempirical PECT model. Eventually the encounters may be resolved by quantum dynamical calculations of the semiclassical or CAQE (classical approach/quantum encounter) type. Simple statistical collision models only distinguish between "hits and misses". In reality the energy transfer efficiency exhibits characteristic fall off with increasing impact parameter b. This b-dependence can be explicitly accounted for in the master equation for the reaction rate coefficient.
Chemical Physics Letters, 1993
Efficient Monte Carlo sampling methods are used to investigate the effect ofthe conservation of energy and angular momentum on energy transfer in Br,+Ar and Br,+Br, collisions. The effect of the conservation of spatial configuration in the collision is also considered. The results show that angular momentum conservation has a small ( 10%20%) but significant restraining effect on the energy transfer rate while the conservation of the spatial configuration reduced it by nearly 50%. The effects of anharmonicity in the bond potential of the diatomic molecule are also studied and found to be significant. Comparison with trajectory calculations reemphasizes the observation that for small molecules the energy transfer approaches the statistical limits only for strong interaction potentials.
The Journal of Chemical Physics, 2013
Quantum scattering calculations of vibration-vibration (VV) and vibration-translation (VT) energy transfer for non-reactive H 2 -H 2 collisions on a full-dimensional potential energy surface are reported for energies ranging from the ultracold to the thermal regime. The efficiency of VV and VT transfer is known to strongly correlate with the energy gap between the initial and final states. In H 2 (v = 1, j = 0) + H 2 (v = 0, j = 1) collisions, the inelastic cross section at low energies is dominated by a VV process leading to H 2 (v = 0, j = 0) + H 2 (v = 1, j = 1) products. At energies above the opening of the v = 1, j = 2 rotational channel, pure rotational excitation of the para-H 2 molecule leading to the formation of H 2 (v = 1, j = 2) + H 2 (v = 0, j = 1) dominates the inelastic cross section. For vibrationally excited H 2 in the v = 2 vibrational level colliding with H 2 (v = 0), the efficiency of both VV and VT process is examined. It is found that the VV process leading to the formation of 2H 2 (v = 1) molecules dominates over the VT process leading to H 2 (v = 1) + H 2 (v = 0) products, consistent with available experimental data, but in contrast to earlier semiclassical results. Overall, VV processes are found to be more efficient than VT processes, for both distinguishable and indistinguishable H 2 -H 2 collisions confirming room temperature measurements for v = 1 and v = 2.
Theory of vibrational energy transfer between simple molecules in nonreactive collisions
Chemical Reviews, 1969
This equation is based on the assumption that variations in Q(t) during the collision are small compared to L. It also implies that the energy transferred to the oscillator is small compared to the incident energy since the latter quantity is assumed independent of the excitation in the oscillator. If this equation is substituted into the second of eq 21, the result is p i +f(Qgo) =-(yA"/L) sech2 (uot/2L) (24) Equation 24 may be solved subject to the initial condition lim [g(t)go] = Bi sin (w t + Si) (25) *
Chemical Physics Letters, 1994
A novel non-active model to correct for the leak of zero-point energy in quasi-classical trajectory calculations is proposed. It consists of eliminating every trajectory that fails to satisfy the zero-point energy requirement of quantum mechanics at the end of the trajectory, and then correct the results using a unified statistical approach which takes into account the relative probabibties of the reactive and non-reactive events. The correction factor assumes a simple analytic form, adding no extra cost to the traditional quasiclassical trajectory approach. Test calculations are presented for the total reactivity of the H+ Oa reaction out of the initial vibrational-rotational state (u, i) = (0, 0), keeping the total angular momentum .I= 0. Comparison of the results with quantum mechanical reactivities calculated on the same (DMBE IV) potential energy surface shows good agreement. A possible generalization of the model to require a local zero-point energy along the trajectory is pointed out.
Possible quantum effects in collisional energy transfer in highly excited molecules
Chemical Physics Letters, 1990
It has been observed that classical trajectory calculations of energy transfer rates in large highly excited molecules with He bath gas give values much higher than experiment. This might be caused by quantum effects in which contributions from higher partial waves do not contribute to energy transfer. Experimental means of testing this postulate are proposed.
Energy transfer in collisions between two vibrating molecules
Chemical Physics Letters, 1985
We study vrbrarional energy transfer in rnelastic collmear collisions betBeen IWO diaromrc molecules The system is represemed by IWO linearly driven parametric oscillators with a bilinear_ time-dependent residua1 coupling between them. We amu& for Ihe time evolution of the Irncarly dnvcn par;lmetric osciilarow with an operator algebra. and use perturbation theory and basis expansions LO include the residual couphng Rcsulls are prcserued Ior H,-FH and N2-CO. Direct twequantum transitions are found to be important even Zor low relst~rr collrs~on enrrgics.