Dynamics of the photodissociation of triplet ketene

Chemical Physics, 2003

Product energy distributions (PEDs) for the photodissociation of acetone at 266, 248, and 193 nm were evaluated by direct classical trajectory calculations on the lowest triplet potential energy surface. CASSCF(8,7) and MRCI+Q calculations were first performed to obtain a set of high-level ab initio data with which the semiempirical parameters were refined. The trajectories were initiated at the barrier, using two different microcanonical sampling methods. The results obtained for the excess energies corresponding to excitation at 266 and 248 nm are in good agreement with the experimental product energy partitioning, supporting a dissociation event taking place on the T1 surface after intersystem crossing from the initially exited S1 state. At 193 nm, the results obtained with the two sampling methods show significant discrepancies. The PEDs calculated with the anharmonic sampling procedure appear to be consistent with the experimental data.

Chemical physics, 1998

For the latter, the PST calculations lead to an average rotational energy in CO which is not compatible with the measured value, thus suggesting that this channel does not represent an important contribution to the dissociation process.

2013

Bibliography 218 Contents v List of Tables xxiii Glossary xxv the absorption of light. Within the framework of non-relativistic quantum mechanics, such a process may be cast in the following form. An initial state |ψ i is taken to propagate on the ground state potential until time t = 0. Taking |ψ i to be an eigenstate of the ground state potential, the initial wavefunction changes only by a phase factor. At time t = 0, the absorption of a single photon results in the promotion of the state |ψ i to an electronically excited state, which, assuming vertical excitation, is given in Photodissociation processes are typically challenging to model in an accurate manner for two primary reasons. Firstly, unlike the preponderance of ground state processes, the excitation of a molecular system to an electronically excited state denies us, in general, the possibility of treating in a satisfactory manner the electronic and nuclear degrees of freedom as being decoupled. Thus, the evolution of the wavepacket |φ i has be considered to occur over a manifold of vibronically coupled electronic states. Secondly, the πσ * , valence-type characters as the the X-H dissociation coordinate is traversed. Explanation of this change in character is typically made by taking the adiabatic potential in question to correspond to an avoided crossing between two diabatic states: a lower, bound 3s Rydberg state that is vibronically coupled to a higher-lying, purely dissociative πσ * state by the X-H

Journal of Chemical Physics, 1995

Calculations of the microcanonical isomerization rates for vibrationally excited ketene are presented. The calculations utilize the quantum reactive scattering methodology of absorbing boundary conditions with a discrete variable representation to obtain the cumulative reaction probability for one form of ketene to isomerize via the oxirene intermediate, and were carried out with model 1-, 2-, and 3-degree-of-freedom potential energy surfaces constructed using ab initio data. Significant differences are seen in the energy dependent features of the microcanonical rate for the single mode and multi-mode potentials; e.g., the single mode potential exhibits tunneling resonances with widths of around 1 cm Ϫ1 , while the calculations involving more than one degree of freedom have additional resonant features that have widths around 10 cm Ϫ1 and also exhibit non-Breit-Wigner resonant line shapes. This suggests that many of the resonance features are best described as Feshbach ͑energy transfer, or dynamical͒ resonances that result because of a strongly bent region on the multi-mode potential energy surfaces. The calculated rates show reasonable qualitative agreement with the experimental results of Lovejoy and Moore ͓J. Chem. Phys. 98, 7846 ͑1993͔͒.

Computer Physics Communications, 1993

A program is presented for calculating the total energy absorption cross-section for the photodissociation of a diatomic molecule. The mechanism is assumed to involve the absorption of a photon of ultraviolet radiation which causes an electronic transition in the diatomic molecule from a bound to a repulsive electronic state. The two atoms then fly apart under the influence of the forces on the repulsive electronic state causing the molecule to break up into its atomic fragments. Time dependent quantum dynamical methods are used in the calculation. These methods yield the complete absorption spectrum from a single solution of the dynamics of the system. The computer program permits the calculation of cross-sections for molecules in different initial vibrational states. The program is self-contained.

Physical Chemistry Chemical Physics, 2013

We present on the fly surface hopping simulations of the dynamics of photoexcited acetone in the n → π * band, taking into account both the spin-orbit and the dynamic couplings and allowing for the CC bond dissociation. The S 0 , S 1 , T 1 and T 2 states were considered and the propagation time was 50 ps. According to the simulation results, after excitation to S 1 both Internal Conversion (IC) to S 0 and InterSystem Crossing (ISC) to T 1 or T 2 take place at comparable rates; T 2 plays an important role and the simultaneous treatment of the spin-orbit and dynamic couplings is shown to be mandatory to describe the photodynamics. We propose a mechanism that explains the observed fast and slow decay rates of the S 1 state of acetone.

International Journal of Quantum Chemistry, 2006

Wave packet simulations using ab initio potential energy surfaces (PES) have been developed within the framework of the constrained Hamiltonian methodology. The approach is presented with the example of bromoacetyl chloride photodissociation.

Chemical Physics Letters, 2002

A time-dependent three-dimensional nonadiabatic computation study of the photodissociation of the van der Waals Na Á Á Á FH molecule was performed for total J ¼ 0. A very low probability of photo-reaction to produce NaF + H was observed from most initial conditions. Enhancement of the NaF + H product was observed for the isotopically substituted Na Á Á Á FD. The three-dimensional calculations are in qualitative agreement with the two-dimensional previous study. Calculated excited state lifetimes were in the range of $100 ps. Excitation of the bend and the van-der Waals stretch significantly shortened these lifetimes without increasing the reaction yield. Ó

The Journal of chemical …, 1991

The rotational distributions of CO products from the dissociation of ketene at photolysis energies 10 cm-' below, 56, 110,200,325,425,1107, 1435, 1720, and 2500 cm-' above the singlet threshold (30 116.2 cm-'), are measured in a supersonic free jet of ketene. The CO(v!' = 0) rotational ...

Chemical Physics Letters, 1995

The photodissociation of ketene with a narrow-band tunable laser has been studied at 218.0, 212.5 and 207.0 nm. A CH photofragment is formed in the C 2E+ (v'= 0), B 2E-(v'= 0, 1) and A 2A (v'= 0, 1) states through a process involving the absorption of two laser photons. The visible emission observed above 580 nm is attributed to the CH2(b 1B 1) photofragrnent formed in a single-photon process. The experimental results strongly suggest that electronically excited CH could be formed in a sequential mechanism involving the absorption of a second photon by the CH2(b 1B 1) intermediate. Nevertheless, the simultaneous existence of several mechanisms must be considered to explain the formation of the CH fragment in the various observed electronic states. 0009-2614/95/$09.50