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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.

Abstract: The theory of thermally induced hopping (TIH) in donor–bridge–acceptor systems for hole transport in DNA duplexes in solution is extended to include energetic theoretical data for the effects of inter-nucleobase interactions. The extended theory incorporates the site specificity of the energetic stabilization of the radical cation of guanine (G), which acts as a resting site for the hole, and of the radical cations of adenine (A), which are accessible by thermal excitation from G+ (Δ =0.20–0.25eV). The modified TIH model properly accounts for the flat bridge size dependence of the relative chemical yields for hole transport in G(A–T) n GGG duplexes (n =4–16). This flat, non-ohmic, bridge length dependence is attributed to an energetic gating mechanism, which is induced by energy barriers (∼0.1eV) exerted by the proximal and by the terminal edge A groups in the (A) n bridge, while the interior A groups act as shallow traps for the hole. Our ‘molecular polaron’ model for incoherent, hopping charge transport in solvated DNA is supported by independent theoretical evidence for hole localization induced by intrabase configurational distortions and by polar solvent effects. [Copyright &y& Elsevier]

Abstract: We establish some relations between the kinetics of incoherent, hopping charge transport in bridged large scale chemical systems or in a single-component duplex DNA, and the electrical properties (electric current (j) and conductance (g)) of these systems connected by two electrodes. We considered two distinct voltage distributions across the equienergetic chain (with N bridge elements, and an intersite hopping rate k), which involve the voltage being biased only across the edge bridge elements (case (i)), and the voltage being equally distributed across the bridge (case (ii)). For sufficiently long chains in the low voltage (Φ) domain, we find that j =(ek/N)G(κ 1,κ −1)(eΦ/k B T), where G() is a function of charge injection rates κ 1(κ −1) to (from) the electrode. The low field (constant) conductance is g =1.6×10−19(k/N)G Ω−1. At high voltages we established the existence of a maximal, constant, Φ independent current (j max), where g →0. For case (i) j max = ek/N, being determined by the intersite hopping rate and by N −1, as appropriate for diffusional charge transport. For case (ii) j max = eκ 1, being independent of the chain length, and determined by the rate of charge injection from the electrode. Finally, we applied our kinetic model for the description of incoherent charge transport in and the electronic properties of a donor–acceptor pair connected by two electrodes. [Copyright &y& Elsevier]

We present a kinetic–quantum model for the mechanisms of hole transport in DNA duplexes, which involves a sequence of hole hopping processes between adjacent guanines (G) and/or hole hopping/trapping via GG or GGG, all of which are separated by thymine (T)–adenine (A) bridges. Individual hole hopping processes between G sites fall into two distinct parallel mechanisms, i.e., unistep superexchange mediated hopping via `short'' (T–A)n bridges and thermally induced hopping (TIH) via `long'' (T–A)n (n>3–4) bridges. The bridge specificity for TIH via (A)n chains pertains to the energetics, with the G+A energy gap Δ=0.20±0.05 eV being sufficiently low to warrant endothermic hole excitation from G+ to (A)n, and to the electronic couplings, with the nearest-neighbor A–A couplings being unique in the sense that the intrastrand and interstrand couplings are close and large (V(A–A)≃0.30–0.060 eV). Accordingly, both effective intrastrand and interstrand (zigzagging) hole transport via (A)n chains will prevail, being nearly invariant with respect to the nucleobases ordering within the (T–A)n duplex. We treated the `transition'' between the superexchange and the TIH mechanism in 5′-G+(T–A)nG-3′ duplexes to predict that the crossover occurs at nx≃3–4, with nx exhibiting a moderate bridge specificity and energy gap dependence. nx is in accord with the experimental data of Giese et al. [Nature 412, 318, 2001]. We assert that the kinetic–quantum mechanical model for the chemical yields and elementary rates cannot be reconciled with the experimental TIH data, with respect to the very weak bridge size dependence of the relative chemical yields and the ratios of the rates. Configurational relaxation accompanying endothermic hole injection from G+ to (A)n may result in the gating (switching-off) of the backrecombination, providing a reasonable description of TIH dynamics and very long-range hole transport in long (A)n chains. [Copyright &y& Elsevier]

Deals with a study which used a kinetic analysis of chemical yield data to establish the occurrence of hole transport via charge hopping and the conditions for the realization of large distances in DNA. Energetic control of charge migration in DNA; Kinetic scheme for hole transport; Maximal distance for hole hopping; Time-resolved information on hole hopping.

We address a central question in the realm of the dynamics of high-n ( = 40- 250) Rydberg states of diatomics and large molecules. What is the coupling responsible for the 'global' l mixing, which results in the breakdown of the n8 scaling law for the non-radiative lifetimes and for the lifetime lengthening (by two to four orders of magnitude) of these states? To explore the implications of intramolecular interactions on l mixing and on electronic-rotational energy exchange we analysed the intramolecular couplings of the ion core dipole, quadrupole and (anisotropic) polarizability with a non-penetrating (l 3) Rydberg electron, in conjunction with the energy gaps between proximal pairs of energy levels. Calculations of the energy gaps and the couplings were performed for the high-n non-penetrating Rydberg states of NO and for model 'light' (B = 19 cm-1) and 'heavy' (B = 0.05 cm-1) polar molecules. All the intramolecular interactions are of the form of a power law proportional to l-eta, with eta being determined by the nature of the long-range coupling, by the l dependence of the quantum defects for multipole couplings and by the l dependence of angular integrals. We established a bottleneck effect for the intramolecular couplings between non-penetrating (l 3) states. For n- and N+-changing dipole, quadrupole and polarizability interactions the energetics ofthe proximalpairs of levels,inconjunctionwiththe bottleneck effect,prohibit the n, l, N+, N> - n', l', N+', N>, l ( 3) couplings (with n n) and the electronic-rotational energy exchange. For n- and N+-conserving quadrupole and polarizability interactions, the l ( 3) mixing (which prevails only for l N++ N) is also prohibited by the bottleneck effect. 'Global' intramolecular l mixing (with both n n' and n = n') in diatomics and in large molecules is precluded, implying that the dramatic lengthening of the non-radiative lifetimes of high-n Rydberg states can be induced only by exterior electric field coupling. [ABSTRACT FROM AUTHOR]

Demonstrates that the solvent dependence of the radiative recombination rates in donor-bridge-acceptor molecules can be quantitatively accounted for in terms of the intensity borrowing from locally excited states. Energy gap dependence of the radiative lifetimes; Oscillator strength for charge-transfer excitation; Electronic coupling between local excitation and the charge transfer state.

Electronic matrix elements for hole transfer between Watson-Crick pairs in desoxyribonucleic acid (DNA) of regular structure, calculated at the Hartree-Fock level, are compared with the corresponding intrastrand and interstrand matrix elements estimated for models comprised of just two nucleobases. The hole transfer matrix element of the GAG trimer duplex is calculated to be larger than that of the GTG duplex. "Through-space" interaction between two guanines in the trimer duplexes is comparable with the coupling through an intervening Watson-Crick pair. The gross features of bridge specificity and directional asymmetry of the electronic matrix elements for hole transfer between purine nucleobases in superstructures of dimer and trimer duplexes have been discussed on the basis of the quantum chemical calculations. These results have also been analyzed with a semiempirical superexchange model for the electronic coupling in DNA duplexes of donor (nuclobases)-acceptor, which incorporates adjacent base-base electronic couplings and empirical energy gaps corrected for solvation effects; this perturbation-theory-based model interpretation allows a theoretical evaluation of experimental observables, i.e., the absolute values of donor-acceptor electronic couplings, their distance dependence, and the reduction factors for the intrastrand hole hopping or trapping rates upon increasing the size of the nucleobases bridge. The quantum chemical results point towards some limitations of the perturbation-theory-based modeling. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]