Topic
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.
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TL;DR: The hypothesis that O-H fission following excitation to the S(1) state involves tunnelling under the S (1)/S(2) CI-in accord with conclusions reached from a recent correlation of the excited state lifetimes of phenol (and many substituted phenols) with the corresponding vertical energy gaps between their S( 1) and S (2) PESs is confirmed.
Abstract: When phenol is photoexcited to its S1 (11ππ*) state at wavelengths in the range 257.403 ≤ λphot ≤ 275.133 nm the O−H bond dissociates to yield an H atom and a phenoxyl co-product, with the available energy shared between translation and well characterised product vibration. It is accepted that dissociation is enabled by transfer to an S2 (11πσ*) state, for which the potential energy surface (PES) is repulsive in the O−H stretch coordinate, RO–H. This S2 PES is cut by the S1 PES near RO–H = 1.2 A and by the S0 ground state PES near RO−H = 2.1 A, to give two conical intersections (CIs). These have each been invoked—both in theoretical studies and in the interpretation of experimental vibrational activity—but with considerable controversy. This paper revisits the dynamic mechanisms that underlie the photodissociation of phenol and substituted phenols in the light of symmetry restrictions arising from torsional tunnelling degeneracy, which has been neglected hitherto. This places tighter symmetry constraints ...
128 citations
TL;DR: In this article, the authors used two-color resonant four-wave mixing (RFWM−SEP) and the more conventional technique in which SEP signals are obtained from fluorescence depletion (FD‐SEP), to measure the vibrational energies, resonance widths, and relative fluorescence intensities.
Abstract: We use dispersed fluorescence (DF) and stimulated emission pumping (SEP) spectroscopies on the B 2A′–X 2A′ system of jet‐cooled HCO to measure the vibrational energies, resonance widths, and relative fluorescence intensities of 73 bound and resonance states supported by the ground‐state potential energy surface. The SEP experiments use both two‐color resonant four‐wave mixing (RFWM‐SEP) and the more conventional technique in which SEP signals are obtained from fluorescence depletion (FD‐SEP). Where applicable, RFWM‐SEP provides superior spectra to those obtained with FD‐SEP, which is susceptible to saturation broadening that can prevent accurate determinations of resonance widths. The observed bound and resonance states span an energy range of 2000–21 000 cm−1 and comprise a wide range of vibrational excitation among the three vibrational modes, including states with 1–12 quanta of excitation in the C–O stretch, 0–5 quanta of bending excitation, and 0–1 quanta of excitation in the C–H stretch. The width...
128 citations
TL;DR: In this article, the authors investigated the unimolecular dissociation of the formyl radical HCO in the electronic ground state using a completely new ab initio potential energy surface, and the dynamics calculations were performed in the timeindependent picture by employing a variant of the log-derivative Kohn variational principle.
Abstract: The unimolecular dissociation of the formyl radical HCO in the electronic ground state is investigated using a completely new ab initio potential energy surface. The dynamics calculations are performed in the time‐independent picture by employing a variant of the log‐derivative Kohn variational principle. The full resonance spectrum up to energies more than 2 eV above the vibrational ground state is explored. The three fundamental frequencies (in cm−1) for the H–CO and CO stretches, and the bending mode are 2446 (2435), 1844 (1868), and 1081 (1087), where the numbers in parentheses are the measured values of Sappey and Crosley obtained from dispersed fluorescence excitation spectra [J. Chem. Phys. 93, 7601 (1990)]. In the present work we primarily emphasize the dissociation of the pure CO stretching resonances (0v20) and their decay mechanisms. The excitation energies, dissociation rates, and final vibrational–rotational state distributions of CO agree well with recent experimental data obtained from stim...
128 citations
TL;DR: In this article, the appearance threshold and yield curve of individual 1CH2 rotational states were obtained by scanning the photolysis laser frequency with a fixed LIF probe laser frequency, and a lower bound of 7×107 s−1 was set for the dissociation rate on the triplet surface at the singlet energy threshold.
Abstract: Ketene (CH2CO) in a supersonic free jet was photodissociated by a tunable pulsed laser in the frequency range just above the threshold for production of singlet methylene, CH2 (a 1A1). CH2 was detected by laser‐induced fluorescence (LIF). The appearance threshold and yield curve of individual 1CH2 rotational states were obtained by scanning the photolysis laser frequency with a fixed LIF probe laser frequency. The dissociation occurs on the ground electronic state potential energy surface. The threshold for CH2CO→1CH2+CO is found to be 30 116.2±0.4 cm−1. By varying the delay between the photolysis and probe pulses, a lower bound of 7×107 s−1 was set for the dissociation rate on the triplet surface at the singlet energy threshold. The yield curves, or photofragment excitation (PHOFEX) spectra, exhibit sharp steps spaced by the CO rotational term values. The experimental data provide a rigorous test of theoretical models of photofragment dynamics. The data clearly show that nuclear spin is conserved throug...
128 citations
TL;DR: In this paper, the potential energy surface (PES) of the protonated water dimer (H5O2+) was derived using the multiconfiguration time-dependent Hartree (MCTDH) method.
Abstract: Quantum-dynamical full-dimensional (15D) calculations are reported for the protonated water dimer (H5O2+) using the multiconfiguration time-dependent Hartree (MCTDH) method. The dynamics is described by curvilinear coordinates. The expression of the kinetic energy operator in this set of coordinates is given and its derivation, following the polyspherical method, is discussed. The PES employed is that of Huang et al. [JCP, 122, 044308, (2005)]. A scheme for the representation of the potential energy surface (PES) is discussed which is based on a high dimensional model representation scheme (cut-HDMR), but modified to take advantage of the mode-combination representation of the vibrational wavefunction used in MCTDH. The convergence of the PES expansion used is quantified and evidence is provided that it correctly reproduces the reference PES at least for the range of energies of interest. The reported zero point energy of the system is converged with respect to the MCTDH expansion and in excellent agreement (16.7 cm-1 below) with the diffusion Monte Carlo result on the PES of Huang et al. The highly fluxional nature of the cation is accounted for through use of curvilinear coordinates. The system is found to interconvert between equivalent minima through wagging and internal rotation motions already when in the ground vibrational-state, i.e., T=0. It is shown that a converged quantum-dynamical description of such a flexible, multi-minima system is possible.
128 citations