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.

H2(v = 0,1) + C+(2 P) → H+CH + state-to-state rate constants for chemical pumping models in astrophysical media

Abstract: State-to-state rate constants for the title reaction are calculated using the electronic ground state potential energy surface and an accurate quantum wave-packet method. The calculations are performed for H{sub 2} in different rovibrational states, v = 0, 1 and J = 0 and 1. The simulated reaction cross section for v = 0 shows a rather good agreement with the experimental results of Gerlich et al., both with a threshold of 0.36 eV and within the experimental error of 20%. The total reaction rate coefficients simulated for v = 1 are two times smaller than those estimated by Hierl et al. from cross sections measured at different temperatures and neglecting the contribution from v > 1 with an uncertainty factor of two. Thus, part of the disagreement is attributed to the contributions of v > 1. The computed state-to-state rate coefficients are used in our radiative transfer model code applied to the conditions of the Orion Bar photodissociation region, and leads to an increase of the line fluxes of high-J lines of CH{sup +}. This result partially explains the discrepancies previously found with measurements and demonstrates that CH{sup +} excitation is mostly driven by chemical pumping.

The dynamics of the hydrogen exchange reaction at 2.20 eV collision energy: Comparison of experimental and theoretical differential cross sections

Abstract: The H+D2(v=0,j=0)→HD(v′,j′)+D isotopic variant of the hydrogen atom exchange reaction has been studied in a crossed molecular beam experiment at a collision energy of 2.20 eV. Kinetic energy spectra of the nascent D atoms were obtained by using the Rydberg atom time-of-flight technique. The extensive set of spectra collected has permitted the derivation of rovibrationally state-resolved differential cross sections in the center-of-mass frame for most of the internal states of the HD product molecules, allowing a direct comparison with theoretical predictions. Accurate 3D quantum mechanical calculations have been carried out on the refined version of the latest Boothroyd–Keogh–Martin–Peterson potential energy surface, yielding an excellent agreement with the experimentally determined differential cross sections. The comparison of the results from quasi-classical trajectory calculations on the same potential surface reveals some discrepancies with the measured data, but shows a good global accordance. The t...

Potential energy surfaces for water dynamics. II. Vibrational mode excitations, mixing, and relaxations

Abstract: Dynamical behavior of liquid water is investigated by analyzing the potential energy surface involved. Multidimensional properties of the potential energy surface are explored in terms of vibrational mode excitations at its local energy minima, called inherent structures. The vibrational mode dynamics, especially mechanism of mode relaxation and structure transitions, is analyzed. It shows very strong excitation energy dependence and mode dependence. There are three kinds of vibrational coupling among modes. For excitations of energy near the room temperature, most modes (more than 90% of total modes) individually interact with only one or two other modes, and yield near recurrence of the mode energy in a few tens picoseconds (very slow relaxation). Spatially localized modes in the intermediate frequency range couple with many delocalized modes, yielding fast relaxation. The coupling is governed by atomic displacement overlaps and frequency matching. Each mode couples with nearby frequency or double frequency modes through the Fermi resonance. Lowest frequency modes almost always lead to transitions from a potential energy well to neighbor potential wells, called inherent structure transitions. In high energy excitation, some intermediate frequency modes also yield such transitions. There exist very low energy paths involving single or few water molecule displacements at almost every inherent structure, indicating that certain facile molecular movements occur even in very low temperature states. Different energy excitations of a low frequency mode result in different inherent structure transitions; transitions caused by high energy excitations involve many large molecular displacements. These inherent structure transitions are the source of the water binding structural reorganization dynamics. Significance of these vibrational mode dynamics in the water dynamics is discussed.

The many ways to have a quintuple bond.

Abstract: The existence and persistence of five-fold (quintuple) bonding in isomers of model RMMR molecules of quite different geometry are examined theoretically. The molecules studied are RMMR, with R = H, F, Cl, Br, CN, and CH3; M = Cr, Mo, and W. The potential energy surface of these molecules is quite complex, containing two, three, even four local minima. The structural preferences in these molecules are rationalized, and electronic factors responsible for these preferences are elucidated. The linear geometry is always a minimum, but almost never the global minimum; there is a definite preference in RMMR for either a trans-bent conformation or perturbations of the trans-bent isomer with at least one of the R groups in a bridging position about the MM bond. The potential energy surface of these RMMR molecules is relatively flat, the lowest energy conformation being that which for a given molecule attains the best compromise between maximization of the MM bonding and minimization of orbital interactions that ar...