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The relationship between the electronic-nuclear level structure, the electronic couplings, and the dynamics of hole hopping transport in DNA is explored. The exploration of the range of applicability and the breakdown of the superexchange mechanism in DNA lay the foundations for the scrutiny of the universality.

A new study investigates two distinct mechanisms for the energetic control and kinetics of hole migration in DNA. The superexchange mechanism and the charge hopping mechanism are examined.

Kinetic analysis of radiative charge recombination in donor-bridge-acceptor molecules reveals the influence of solvent polarity on radiative decay rate. Intensity borrowing from locally excited states explain solvent dependence of experimental radiative rates that begin from the solvent shift of the vertical energy gap. Kinetic studies help determine electronic coupling between local excitation and the change transfer state.

In this paper we present a theoretical study of the predissociation dynamics of the nf(N+=2) (with the principal quantum numbers n=40–95) and the np(N+=0) (n=70–125) Rydberg series of NO, which exhibit a marked lifetime dilution (lengthening) at n>=65 for the f series and at n>=116 for the p series [M.J.J. Vrakking and Y. T. Lee, J. Chem. Phys. 102, 8818 (1995)]. The multichannel effective Hamiltonian with several doorway (for excitation) and escape (for decay) states was constructed using experimental information on the quantum defects and on the decay width constants incorporating both intramolecular coupling and exterior electric field coupling between high Rydbergs. The analysis of the intramolecular Rydberg electron–core dipole long range coupling (HR-D) in conjunction with the energy gaps between proximal pairs of energy levels, which are subjected to appropriate selection rules, reveals that (i) for low l(≤3) core-penetrating Rydbergs only a small number of accidental near-resonances are exhibited, and (ii) for high l(>=3) nonpenetrating Rydbergs the electron-core dipole coupling decreases fast with increasing l, i.e., (HR-D)∝l-7. The general characteristics of the high l(>=3) manifold establish a bottleneck effect, which precludes intramolecular l mixing, implying that high Rydberg lifetime dilution effects can be induced only by exterior electric field coupling (HSTARK). Parameter-free multichannel effective Hamiltonian calculations were conducted under narrow-band excitation conditions, which interrogate the electric field induced mixing in the energetic vicinity of the doorway state. The electric field induced l mixing model accounts semiquantitatively for the electric field dependence of the energy-resolved line shapes of the nf(N+=2) series and for the n and electric field dependence of the lifetimes of the nf(N+=2) and the np(N+=0) series. Accidental near-resonant simultaneous intramolecular and electric field... [ABSTRACT FROM AUTHOR]

In this paper we present a theoretical study of the autoionization dynamics of high 2P1/2np′[3/2]1 Rydbergs (with the principal quantum numbers n=100–280) of Ar in weak homogeneous electric fields (F=0.01–1.0 V/cm), which were experimentally interrogated by time-resolved zero-electron kinetic energy (ZEKE) spectroscopy [M. Mühlpfordt and U. Even, J. Chem. Phys. 103, 4427 (1995)], and which exhibit a marked dilution (i.e., ∼2 orders of magnitude lengthening) of the lifetimes relative to those inferred on the basis of the n3 scaling law for the spectral linewidths of the np′ (n=12–24) Rydbergs. The multichannel effective Hamiltonian (Heff) with several doorway state(s) (for excitation and decay) and pure escape states (for decay) was advanced and utilized to treat the dynamics of the mixed Stark manifold of the ZEKE Rydbergs. Heff of dimension 2n-1 is then constructed for a n Rydberg manifold using independent experimental information on the (l dependent) quantum defects δ(l) and the (l, K, J dependent) decay widths, which are of the form Γ0(lKJ)/(n-δ(l))3, with Γ0(lKJ) being the decay widths constants. Here, l, K, and J are the azimuthal, the electronic and the total electronic angular momentum quantum numbers, respectively. Two coupling ranges are distinguished according to the strength of the reduced electric field F(n,p′)=(F/V cm-1)n5/ 3.4×109[δ(p′)(mod1)].Range (A); The onset of the effective coupling of the doorway and escape states, i.e., 0.7≤F(n,p′)≤2. Range (B); The strong mixing domain F(n,p′)≥3. The lifetimes in range (B) can be well represented by a nearly democratic mixing of all the doorway and escape states (lKJ), with the average value <τ(n)>[bar_over_tilde:_approx._equal_to]<τSM(n)>= 2n4h/[J(lJK)Γ0(lJK)]. In range (B) <τ(n)> increases with increasing n and is only weakly F dependent... [ABSTRACT FROM AUTHOR]

In this paper we explore the level structure, the optical excitation modes and the dynamics of a mixed Stark manifold of very high Rydberg states (with principal quantum numbers n=80–250) of large molecules, e.g., 1,4 diaza bicyclo [2,2,2] octane (DABCO) and bis (benzene) chromium (BBC) [U. Even, R. D. Levine, and R. Bersohn, J. Phys. Chem. 98, 3472 (1994)] and of autoionizing Rydbergs of atoms [F. Merkt, J. Chem. Phys. 100, 2623 (1994)], interrogated by time-resolved zero-electron kinetic energy (ZEKE) spectroscopy. We pursue the formal analogy between the level structure, accessibility and decay of very high Rydbergs in an external weak (F[bar_over_tilde:_approx._equal_to]0.1–1 V cm-1) electric field and intramolecular (interstate and intrastate) relaxation in a bound molecular level structure. The onset n=nM of the strong mixing (in an external field F and in the field exerted by static ions) of a doorway state, which is characterized by a low azimuthal quantum number l, a finite quantum defect δ, and a total nonradiative width Γs[bar_over_tilde:_approx._equal_to]Γ0/n3, with the inactive high l manifold is specified by nM[bar_over_tilde:_approx._equal_to]80.6δ1/5(F/V cm-1)-1/5. At n≥nM the level structure and dynamics are characterized by the product γρ, where ρ is the density of states and γ=ΓsD(n) is the average decay width of the eigenstates, with the dilution factor D(n)≊n-2 for (lml) mixing and D(n)[bar_over_tilde:_approx._equal_to]n-1 for (l) mixing, whereupon γρ=(Γ0/4δR)(nM/n)5, being independent of D(n).The sparse level structure is realized for γρ<1, while the dense level structure prevails for γρ>=1, resulting in two limiting situations; (a) a dense limit for n≥nM and a sparse limit for n>nM, and (b) a sparse limit for all n≥nM. The experimental... [ABSTRACT FROM AUTHOR]

In this paper we explore the interrelationship between the energetics and the thermodynamic properties of molecular clusters. We advance simple models for the energy spectrum, which are used to derive analytical results for the thermodynamic properties of these clusters. The energy spectrum is characterized by the distribution of the energies of the local minima of the nuclear potential energy hypersurface, i.e., the inherent structures. On each of these energy levels the vibrational density of states of the particular inherent structure is superimposed. The energy spectra were specified in terms of the energy gap, Δ, between the (single) ground state and the excited-state inherent structures, the number, R, of the inherent structures and their energetic spread W. Four classes of energy spectra were considered. (1) A large energy gap with nearly degenerate excited-state manifold, i.e., Δ>W. (2) A large energy gap with a considerable spread of the excited-state manifold, i.e., Δ≪W and W/R≪Δ. (3) A gapless spectrum with W/R>=Δ. (4) A multiple bunched spectrum with several energy gaps. Explicit analytical relations for the temperature dependence of the internal energy were derived for energy spectra of types (1), (2), and (3) both for the canonical and for the microcanonical ensembles. For energy spectra of types (1) and (2) the caloric curve exhibits a single inflection, which marks the ‘‘transition’’. A unified description of multistate isomerization with large R, which corresponds to rare-gas clusters, and of molecular isomerization with R[bar_over_tilde:_approx._equal_to]1, which prevails for alkali-halide clusters, was provided. For energy spectra of type (3) the transition disappears, while for energy spectra of type (4) hierarchical isomerization is exhibited. Our analytical models have established the ensemble dependence of the transition for types (1) and (2), which is manifested by... [ABSTRACT FROM AUTHOR]

Explores the energetic control of sequential and superexchange electron transfer (ET) mechanisms. Quantum-mechanical simulations and calculations for long-range ET in DBA systems; Separation of the donor and the acceptor by a bridge; ET dynamics in a Franck-Condon (FC) system; Multi-dimensional displaced harmonic potential surfaces; Superposition of superexchange and sequential mechanisms.

Explores the temporal vibrational coherence effects in nonadiabatic radiationless transitions between two electronic states in a large molecule or in the condensed phase. Role of the vibrational quasicontinuum of the final states; Treatment of the final evolution of the wave packet of states.

Electronic matrix elements for hole transfer between adjacent nucleobases in DNA are calculated. The calculated intrastrand hole transfer matrix elements between adjacent thymines, v+(T, T)=0.16 eV, is seen to be in line with the results of the experiments.