Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

Infrared Spectrum of the Protonated Water Dimer in the Gas Phase

Abstract: The frequency-dependent gas-phase infrared multiple photon dissociation (IRMPD) spectrum for the proton-bound dimer of water is reported. The present spectrum is shown to be only in fair agreement with a spectrum reported in an earlier communication but is in agreement with spectra predicted by theoretical means. Two different possible assignments of the observed infrared bands are provided. The first is based on the harmonic oscillator approximation from density functional theory calculations, and a second is based on a quantum four-dimensional model calculation of anharmonic frequencies and intensities. Both calculated spectra agree fairly well, but the density functional calculation assignments are in better agreement. This is expected despite the anharmonic nature of the asymmetric stretch due to the flat potential energy surface associated with this mode.

Comparison of quantum dynamics and quantum transition state theory estimates of the H + CH4 reaction rate.

Abstract: Thermal rate constants are calculated for the H + CH(4) --> CH(3) + H(2) reaction employing the potential energy surface of Espinosa-Garcia (Espinosa-Garcia, J. J. Chem. Phys. 2002, 116, 10664). Two theoretical approaches are used. First, we employ the multiconfigurational time-dependent Hartree method combined with flux correlation functions. In this way rate constants in the range 225-400 K are obtained and compared with previous results using the same theoretical method but the potential energy surface of Wu et al. (Wu, T.; Werner, H.-J.; Manthe, U. Science 2004, 306, 2227). It is found that the Espinosa-Garcia surface results in larger rate constants. Second, a harmonic quantum transition state theory (HQTST) implementation of instanton theory is used to obtain rate constants in a temperature interval from 20 K up to the crossover temperature at 296 K. The HQTST estimates are larger than MCTDH ones by a factor of about three in the common temperature range. Comparison is also made with various tunneling corrections to transition state theory and quantum instanton theory.

Ab initio calculation of a global potential, vibrational energies, and wave functions for HCN/HNC, and a simulation of the (A-tilde)-(X-tilde) emission spectrum

Abstract: We present a potential energy surface for the HCN/HNC system which is a fit to extensive, high quality ab initio, coupled‐cluster calculations. The new surface is an improved version of one that was reported previously by us [J. A. Bentley, J. M. Bowman, B. Gazdy, T. J. Lee, and C. E. Dateo, Chem. Phys. Lett. 198, 563 (1992)]. Exact vibrational calculations of energies and wave functions of HCN, HNC, and delocalized states are done with the new potential using a new method, which combines a truncation/recoupling method in a finite basis representation procedure with a moveable basis to describe the significant bend–CH stretch correlation. All HCN and HNC states with energies below the energy of the first delocalized state are reported and characterized. All delocalized states up to 18 347 cm−1 above the HCN zero‐point energy and higher energy localized HCN states are also reported and characterized. Vibrational transition energies are compared with all available experimental data on HCN and HNC, including high CH‐overtone states up to 23 063 cm−1. We also report a simulation of the A–X stimulated emission pumping (SEP) spectrum, and compare the results to experiment. The simulation is performed within the Franck–Condon approximation, and makes use of 400 even‐bend wave functions for the ground electronic state, and a realistic vibrational wave function for the first excited bend state in the excited A state. The potential for the A state is slightly modified, relative to one implied by a previously reported force field, to improve agreement with the experimental fundamentals for the A state. In addition, the A‐state wave function is adjusted slightly to improve agreement with the SEP spectrum. We also report Franck–Condon factors for odd bending states of HCN, with one quantum of vibrational angular momentum, in order to compare with the recent assignment by Jonas, Yang, and Wodtke [J. Chem. Phys. 97, 2284 (1992)], based on axis‐switching arguments of a number of previously unassigned states in the SEP spectrum.

A global H2O potential energy surface for the reaction O(1D)+H2→OH+H

Abstract: A global, single‐valued ground‐state H2O potential surface for the reaction O(1D)+H2→OH+H has been constructed from a new set of accurate ab initio data using a general multidimensional interpolation method. The ab initio calculations are of the multireference, configuration interaction variety and were carried out using augmented polarized triple zeta basis sets. The multidimensional method is formulated within the framework of the reproducing kernel Hilbert space theory. The H2O potential is expressed as a many‐body sum of a single one‐body term, three two‐body terms, and a single three‐body term. The one‐body term is the dissociation energy to the three‐atom limit 2H(2S)+O(3P). The two‐body terms are two O–H and one H–H adiabatic diatomic potentials of lowest energy. Each diatomic term is obtained by interpolating a discrete set of ab initio data using a one‐dimensional, second‐order, distancelike reproducing kernel. The three‐body term is obtained by interpolating the difference of the H2O ab initio d...

Accurate quantum calculation for the benchmark reaction H2+OH→H2O +H in five‐dimensional space: Reaction probabilities for J=0

Abstract: A time‐dependent wave packet method has been employed to compute initial state‐specific total reaction probabilities for the benchmark reaction H2+OH→H2O+H on the modified Schatz–Elgersman potential energy surface which is derived from ab initio data In our quantum treatment, the OH bond length is fixed but the remaining five degrees of freedom are treated exactly in the wave packet calculation Initial state‐specific total reaction probabilities for the title reaction are presented for total angular momentum J=0 and the effects of reagents rotation and H2 vibration on reaction are examined