Intersection Of Potential Energy Surfaces Research Articles

Nuclear wavepacket motion producing a reversible charge separation in bacterial reaction centers

The excitation of bacterial reaction centers (RCs) at 870 nm by 30 fs pulses induces the nuclear wavepacket motions on the potential energy surface of the primary electron donor excited state P*, which lead to the fs oscillations in stimulated emission from P* [M.H. Vos, M.R. Jones, C.N. Hunter, J. Breton, J.-C. Lambry and J.-L. Martin (1994) Biochemistry 33, 6750–6757] and in Q Y absorption band of the primary electron acceptor, bacteriochlorophyll monomer B A [A.M. Streltsov, S.I.E. Vulto, A.Y. Shkuropatov, A.J. Hoff, T.J. Aartsma and V.A. Shuvalov (1998) J. Phys. Chem. B 102, 7293–7298] with a set of fundamental frequencies in the range of 10–300 cm −1. We have found that in pheophytin-modified RCs, the fs oscillations with frequency around 130 cm −1 observed in the P*-stimulated emission as well as in the B A absorption band at 800 nm are accompanied by remarkable and reversible formation of the 1020 nm absorption band which is characteristic of the radical anion band of bacteriochlorophyll monomer B A −. These results are discussed in terms of a reversible electron transfer between P* and B A induced by a motion of the wavepacket near the intersection of potential energy surfaces of P* and P +B A −, when a maximal value of the Franck–Condon factor is created.

Location of conical intersections by the Pancharatnam connection and the sign-change theorem of Longuet-Higgins: a model calculation with the H4 potential surface

We present new methods to locate conical intersections of potential energy surfaces using the Pancharatnam connection and the Longuet-Higgins' sign-change theorem. We have applied the new methods to locate conical intersections for the H4 potential surface that are constructed by the valence-bond wave functions. The potential energy surface is rich in conical intersections that are not isolated in general but seen in the form of a seam or higher dimensional geometrical object. The `pair annihilation of conical intersections', i.e., the disappearance of two conical intersections by merging into a Renner–Teller crossing and successive lifting of the Renner–Teller crossing is observed.

Chemical "Double Slits": dynamical interference of photodissociation pathways in water

Photodissociation of water at a wavelength of 121.6 nanometers has been investigated by using the H-atom Rydberg tagging technique. A striking even-odd intensity oscillation was observed in the OH(X) product rotational distribution. Model calculations attribute this oscillation to an unusual dynamical interference brought about by two dissociation pathways that pass through dissimilar conical intersections of potential energy surfaces, but result in the same products. The interference pattern and the OH product rotational distribution are sensitive to the positions and energies of the conical intersections, one with the atoms collinear as H-OH and the other as H-HO. An accurate simulation of the observations would provide a detailed test of global H(2)O potential energy surfaces for the three (&Xtilde;/A/&Btilde;) contributing states. The interference observed from the two conical intersection pathways provides a chemical analog of Young's well-known double-slit experiment.

Topographical Features of Potential Energy Surfaces of the B + O2 Chemical Reaction

Reactivities of spin−orbit states in B(2P1/2, 3/2) + O2(X ) → BO(X 2Σ+, A 2Π) + O(3PJ) have been studied by fluorescence imaging techniques. From experimentally measured reactivities of the 2P1/2 and 2P3/2 spin−orbit states of B atoms toward O2 molecules and model calculations, an avoided intersection of potential energy surfaces in the entrance valley can be deduced. From the A → X chemiluminescent spectra of BO* products under crossed beam conditions, the spatial patterns of BO* chemiluminescences, and fluorescence imagings of ground state BO radicals, it was inferred that both vibrationally excited BO(X 2Σ+) and electronically excited BO(A 2Π) products are formed in the B + O2 reaction. The reaction channel that leads to the formation of A state BO* correlates solely with B atoms in the 2P3/2 spin−orbit state. On the other hand, half of the population of this 2P3/2 level can cross efficiently to a ground state reaction channel, in which the formation of X state BO correlates adiabatically with B atoms ...

Quantum scattering on the Σ-Π intersection of potential energy surfaces

Quantum nonadiabatic scattering on three potential energy surfaces characterized by a single intersection point of the conic type is considered. The angular distribution of the products and cross section energy dependences for the different channels are calculated. The results are compared with those calculated by the trajectory surface hopping method. It is shown that for high nonresonant energies the trajectory surface hopping method does not give a quantitative and for resonant energies not even a qualitative description of the angular distribution.

Systematic determination of intersections of potential energy surfaces using a Lagrange multiplier constrained procedure

Two nonrelativistic Born-Oppenheimer potential energy surfaces of distinct space-spin symmetry intersect on a surface of dimension N-1 where N is the number of internal nuclear degrees of freedom. Characterization of this entire surface can be quite costly. An algorithm, employing multiconfiguration self-consistent-field (MCSCF)/configuration interaction (CI) wave functions and analytic gradient techniques, is presented which avoids the determination of the full N-I dimensional surface, while directly locating portions of the crossing surface that are energetically important

On the intersection of potential energy surfaces in charge transfer reactions: A crossing seam for two states of the same symmetry in the reaction H++NO(X 2Π)→H(2S)+NO+(X 1Σ+)

An actual crossing seam of two potential energy surfaces of the same symmetry relevant to the charge transfer reaction H++NO(X 2Π)→H(2S)+NO+(X 1Σ+) is reported. This crossing seam occurs for general Cs geometries. It represents the intersection of the 1,2 2A′ potential energy surfaces which correlate asymptotically with H(2S)+NO+(X 1Σ+) and H++NO(X 2Π), respectively. A portion of the seam is exoergic relative to the reactant channel, H++NO(X 2Π), asymptote. The present results complement a previous determination of two allowed crossing seams in C∞v symmetry, and provide, for the first time, an example of a system for which both allowed and actual conical intersections exist. Since the actual crossing seam occurs for geometrical configurations quite distinct from the allowed crossing seams previously considered these results have important implications for the rotational–vibrational energy distribution in the products of the charge exchange process.

Molecular beam chemiluminescence XI: kinetic and internal energy dependence of the NO + O 3 → NO 2*,→ NO 2‡ reaction

Seeded supersonic NO beams were used to study the kinetic energy dependence of both the electronic (NO 2 *) and vibrational (NO 2 ‡) chemiluminescence of the NO + O 3 reaction. In addition the electronic CL is found to be enhanced by raising the NO internal temperature. This is shown to be due to enhanced reactivity of the NO( 2Π, 3 2 ) fine structure component. By difference NO( 2Π 1 2 ) is concluded to yield predominantly groundstate NO 2 ‡. The excitation function for NO 2 * formation from NO( 2Π 3 2 ) is of the form σ 3 2 ( E) = C(E/E 0 - 1) n over the 3–6 kcal energy range where n = 2.4 ± 0.15, C = 0.163 Å 2 and E 0 = 3.2 ± 0.3 kcal/mole. Vibrational IR emission from NO 2 ‡ has an energy dependence different from electronic NO 2 * emission, confirming that emitters are formed predominantly in distinct reaction channels rather than via a common precursor (either NO 2 * or NO 2 ‡). The short wavelength cutoff of the CL spectra recorded at elevated collision energies E ⩽ 15 kcal/mole corresponds to the total available energy. These and literature results are discussed in the light of general properties of the (generally unknown) ONO 3 potential energy surfaces. The formation of electronically excited NO 2 * rather than energetically preferred O 2 ( 1 Δg) (Gauthier and Snelling) can be rationalized in terms of surface hopping near a known intersection of potential energy surfaces more easily than by vibronic interaction in the asymptotic NO 2 product.

More on the multidimensional surface intersection problem and classical trajectory surface hopping

We respond to the previous Comment by Mead and Truhlar pointing out a circularity in our published analysis of a trajectory passing through a locally avoided intersection of potential energy surfaces in a two state system. We did not distinguish clearly in that analysis between properties of the physical system and those of our model for it. Our ‘‘reduction’’ to a one-dimensional problem is rather a ‘‘mapping’’ onto a one-dimensional model. We present a clearer description of the actual procedures we used to demonstrate that our method is valid for the types of systems to which we have applied it.

Spin-orbit coupling and the intersection of potential energy surfaces in polyatomic molecules

Longuet-Higgins’ theorem, which shows that the existence of intersections between potential energy surfaces may be deduced from the behaviour of the wavefunction at points remote from the intersection, is generalized to cover cases where the Hamiltonian is complex. It is concluded that an intersection due to symmetry in one region of nuclear configuration space may imply that the same surfaces intersect over a region of higher dimen­sion and lower symmetry where their wavefunctions belong to the same symmetry species. It is shown that this behaviour occurs in d 1 octahedral complexes in the presence of spin-orbit coupling.

The intersection of potential energy surfaces in polyatomic molecules

It is proved that if the wave function of a given electronic state changes sign when transported adiabatically round a loop in nuclear configuration space, then the state must become degenerate with another one at some point within the loop. I t is further shown that this condition is satisfied by certain unsymmetrical triatomic systems, thereby disposing of a recent claim that the non-crossing rule for diatomic molecules applies also to polyatomic molecules.

Avoided intersection of potential energy surfaces: The (H+ + H2, H + H2+) system

Nonempirical electronic structure calculations have been carried out on the two lowest 1A1 states of H 3+. When one proton is infinitely separated from the other two, these 1A1 potential surfaces cross each other. The nature of this avoided intersection is examined by means of potential curves, contour diagrams, and perspective plots. Surface hopping is discussed within a Landau-Zener-Stuckelberg (LZS) framework and the LZS assumptions concerning the surfaces are shown to be reasonable near the avoided intersection. Ab initio LZS parameters are compared with those obtained from the semiempirical diatomics-in-molecules surfaces of Preston and Tully. The agreement is good, better than might have been anticipated.

Correlation between the Luminescence Behavior of Octahedral Chromium(III) Complexes and the Ligand-Field Strength

An empirical rule for the type of luminescence (fluorescence only, fluorescence and phosphorescence, phosphorescence only) to be expected, which depends on the position of the respective ligands in the spectrochemical series, has been found for octahedral chromium (III) complexes. This correlation is discussed in terms of the shape and intersection of potential-energy surfaces.

Intersection of potential energy surfaces in polyatomic molecules

Intersection of potential energy surfaces in polyatomic molecules