Electronic-vibrational Energy Transfer Research Articles

Effect of Nitrogen Addition on Electron Density and Temperature of Cascaded Arc Argon Discharge Plasma Diagnosed by Laser Thomson Scattering

The electron density and electron temperature of the recombining argon plasma from a cascaded arc discharge source were measured by the laser Thomson scattering approach. In this paper, a small amount of nitrogen gas was introduced into the argon discharge source. The addition of the nitrogen gas was applied to investigate the change of the plasma parameters in terms of electron density and temperature. The measurements showed that the electron density dropped by 2 orders of magnitude at 10% nitrogen gas addition compared with no nitrogen addition. The dissociative recombination following the charge transfer between atomic ions and nitrogen molecules was responsible for the decrease of electron density. In addition, with the increase of nitrogen gas addition, the measurements indicated that the electron temperature first increased to a maximum and then decreased. This was due to that the superelastic collision between the electrons and the highly excited vibrational nitrogen molecules could heat the electrons leading to the increase of electron temperature while the electron-vibrational energy transfer by electron–nitrogen molecules impact excitation resulted in that electron temperature decreased due to electrons’ kinetic energy losing processes.

Effects of Herzberg-Teller vibronic coupling on coherent excitation energy transfer.

In this work, we study the effects of non-Condon vibronic coupling on the quantum coherence of excitation energy transfer, via the exact dissipaton-equation-of-motion evaluations on excitonic model systems. Field-triggered excitation energy transfer dynamics and two dimensional coherent spectroscopy are simulated for both Condon and non-Condon vibronic couplings. Our results clearly demonstrate that the non-Condon vibronic coupling intensifies the dynamical electronic-vibrational energy transfer and enhances the total system-and-bath quantum coherence. Moreover, the hybrid bath dynamics for non-Condon effects enriches the theoretical calculation, and further sheds light on the interpretation of the experimental nonlinear spectroscopy.

The calculation of quenching rate coefficients of O2 Herzberg states in collisions with CO2, CO, N2, O2 molecules

The removal rates of Herzberg states of molecular oxygen O2(c1Σu-, v=0–16), O2(A′3Δu, v=0–11), O2(A3Σu+, v=0–10) in the collisions with ground-state CO2, CO, N2, O2 molecules are calculated according to analytical expressions. The study includes a consideration of intramolecular electron energy transfers without and with vibrational excitation of target molecules and intermolecular processes. The preliminary calculations show important role of electronic–vibrational energy transfer processes in the quenching O2(A3Σu+, v)+CO2; O2(c1Σu-, v)+CO2, CO, N2; O2(A′3Δu, v)+O2. Reasonable agreement of the calculated rate coefficients with data of laser experimental measurements is obtained.

The calculations of quenching rate coefficients of O2(b1g+, v) in collisions with O2, N2, CO, CO2 molecules

The removal rates of singlet molecular oxygen O2(b1Σg+,v=0–15) in the collisions with O2(X3Σg−,v=0–4), N2(X1Σg+,v=0–4), CO(X1Σ+,v=0–4) molecules are calculated according to analytical expression based on Rosen–Zener approximation. The calculations consider electronic-vibrational energy transfer processes in the removal. The study of the quenching of O2(b1Σg+,v) molecules by CO2 includes a consideration of both electronic-vibrational and vibrational–vibrational energy transfer processes. The calculated quenching rate coefficients for the collisions O2(b1Σg+,v)+CO2 show good agreement with available experimental data in the dependence on vibrational levels and temperature.

Predictive modeling of the vibrational quenching in emitting lanthanides complexes

Organic complexes of lanthanides trivalent ions such as Nd3+ and Er3+ are receiving increasing attention in view of their use as dopants in polymeric telecommunication devices. Their employment is however currently limited by their small emission quantum yield (QY) due to non-radiative deactivation of near infrared (NIR) transitions through electronic-vibrational energy transfer (ET). A complete modeling of this quenching effect is presented here and successfully tested on a purpose-made Er3+ complex. This method provides “a priori” information/predictions regarding the emission properties of new complexes thus establishing useful guidelines for the design and synthesis of new molecules and for the engineering of materials suitable in technological applications.

Implications and Applications of Current-Induced Dynamics in Molecular Junctions

Instances of strongly nonadiabatic electronic-vibrational energy transfer have been studied since the early days of quantum mechanics and remain a topic of fundamental interest. Often such transfers are associated with electronic resonances, temporary states where transient localization of charge on the molecule provides a mechanism for channeling electronic energy into vibrational excitation. Extensively studied in the gas phase, electron resonance scattering also occurs with surface adsorbed molecules, where it manifests itself in broadened cross sections and desorption of adsorbates from metal surfaces. In this Account, we focus on a related topic: the implications of nonadiabatic, resonance-mediated scattering to the exciting field of molecular electronics. In this context, researchers can induce directed nuclear dynamics and control these processes in single molecules in contact with metallic and semiconducting electrodes. We discuss a variety of consequences and applications of current-driven nuclear excitation in molecular devices, ranging from the design of new forms of molecular machines to surface chemistry at the single-molecule level and atom-resolved lithography. We highlight two specific examples of molecular nanomachines. In the first, a Au-C(60)-Au transistor, the current induces the oscillatory motion of the center-of-mass coordinate of the C(60). The second, a zwitterion-based rattle, demonstrates excitation of intramolecular motion as the positively charged moiety is threaded back and forth through the negatively charged carbon ring. Finally, we discuss the current-induced desorption of organic molecules from Si(100) both to suggest the potential for controlled surface nanochemistry and to develop guidelines for the design of stable molecular junctions. Modeling the exchange of energy between tunneling electrons and the vibrational degrees of freedom of a target molecule subject to bias voltage, open boundary conditions in the electronic subspace, and the dissipative effects of the electrodes poses a fascinating challenge to contemporary theories of inelastic electron transport. A scattering theory of density matrices is motivated by the need to address large amplitude, chemically relevant dynamics in tandem with an appropriate treatment of the electronic scattering problem. We provide a qualitative discussion of the theory and note the limits in which it reduces to well-known approaches.

Vibrational overtones quenching of near infrared emission in Er3+ complexes

Erbium organic complexes are receiving increasing attention in view of their application in polymeric telecommunication devices, but their use is limited by small emission quantum yield. Non-radiative deactivation of near IR (NIR) transition in Er3+ organic complexes is discussed on the basis of the electronic–vibrational energy transfer. Relevant transition matrix elements necessary to predict quenching effects exerted by various bonds located in the Er3+ coordination sphere are evaluated on the basis of an anharmonic Morse oscillator model and expressed as analytical functions of the fundamental vibrational intensities. The latter are calculated on the basis of various ‘ab initio’ quantum chemical methods, which yield intensity values close to the experimental measurements. Quenching effects in complexes containing a number of common ligands are evaluated and discussed, and a strategy to design highly efficient NIR emitters is proposed.

Polarization of phosphorescence transitions and probabilities of intramolecular nonradiative deactivation of the lowest triplet state of aromatic molecules

This study continues the experimental testing of the validity of the inductive resonance theory of dipole-dipole energy transfer from the T 1→S 0 transition dipole to stretching vibrations of intramolecular CH bonds of naphthalene and its hydroxy derivatives. To this end, in the series of compounds under study, the range of variation of the geometrical parameter [Φ(CH)]2 of the Forster theory, which accounts for the mutual orientation of the energy donor and acceptor, is estimated. Preliminarily, the angles between the transition dipole moments of the radiative and absorptive electronic transitions (T 1→S 0 and S 0→S 1; T 1→S 0 and S 0→S 2; S 1→S 0 and S 0 →S 1; and S 1→S 0 and S 0→S 2) are measured at 77 K by the method of polarization photoselection. From the polarization measurements, the angles between the phosphorescence transition dipole moment and the plane of a molecule are determined. It was found that, upon passage from naphthalene to its β derivatives, the orientation of the dipole moment of the radiative T 1→S 0 transition relative to the plane of a molecule markedly changes, with the in-plane component of the dipole moment being increased by an order of magnitude. The experimentally determined rate constants of nonradiative deactivation of the T 1 state averaged over the CH groups of the naphthalene ring system, k nr(CH), are compared with the rate constants [Φ(CH)]2 of the inductive resonance energy transfer from the dipole of the T 1→S 0 transition to the dipole of the CH vibrations polarized in the plane of a molecule, calculated with regard to the orientational factor [Φ(CH)]2. This comparison showed that, in the series of compounds under study, a change in the orientation of the dipole moment of the radiative T 1→S 0 transition relative to the plane of a molecule does not affect the rate of the nonradiative T 1⇝S 0 transition. This inference is confirmed by the absence of a correlation between the rate constants k dd(CH) calculated by us (with regard to [Φ(CH)]2) and the well-known rate constants k nr(CH) of individual sublevels of the T 1 state measured at T≤1.35 K for a number of organic molecules. The possible sources of discrepancy between the experimental data that k nr(CH) is independent of [Φ(CH)]2 and the predictions of the theory are considered. A conclusion is made that the electronic-vibrational energy transfer between electric dipoles is the most probable mechanism of the T 1⇝S 0 transitions, but the rate constant of the dipole-dipole energy transfer upon interaction of the electronic and vibrational dipoles in a molecule does not depend on their orientations.

An inelastic threshold in electron - alkali cluster collisions

An analysis of integral cross sections for slow electron collisions with neutral sodium clusters and nanoparticles reveals that, in addition to an effective negative ion formation channel, there exists a strong inelastic threshold-type process which appears above a collision energy of 1-1.3 eV. We show that it can be plausibly associated with the onset of direct electron-induced cluster fragmentation. This result highlights the importance of understanding the dynamics of electron-vibrational energy transfer in nanoclusters, including the relative probability of direct vs. statistical energy transfer.

Interaction and energy transfer between divalent Sm ions andCN−molecular defects in KCl

We studied the mutual interaction and electronic-vibrational energy transfer processes between divalent samarium ions and neighboring ${\mathrm{CN}}^{\ensuremath{-}}$ molecular impurities in KCl by the highly site-selective technique of combined excitation-emission spectroscopy as well as by vibrational ${\mathrm{CN}}^{\ensuremath{-}}$ luminescence (VL). We found for ${\mathrm{Sm}}^{2+}\ensuremath{-}{\mathrm{CN}}^{\ensuremath{-}}$ complexes involving just a single ${\mathrm{CN}}^{\ensuremath{-}}$ molecule that the spectral shifts of the intraconfigurational $(4f\ensuremath{\leftrightarrow}4f)$ transitions are very small, and are about 10 times bigger for the interconfigurational ${(4f}^{6}\ensuremath{\leftrightarrow}{4f}^{5}{5d}^{1})$ transitions. No measurable energy transfer from the electronic excitation into the vibrational ${\mathrm{CN}}^{\ensuremath{-}}$ stretch mode takes place for those centers, reflecting the weakly interacting character of the energetically lowest excited ${}^{5}{D}_{0}$ state which belongs to the $4f$-electronic configuration. However, for more complex centers which appear for higher ${\mathrm{CN}}^{\ensuremath{-}}$ concentrations and involve more than one ${\mathrm{CN}}^{\ensuremath{-}}$ molecule the more strongly coupled $5d$-type states are shifted to lower energy, even below the ${}^{5}{D}_{0}$ state. In this case $E\ensuremath{-}V$ energy transfer can be observed by the appearance of VL.

Electronic-Vibrational Energy Transfer between F-Centers and OH<sup>-</sup> Impurities in Alkali Halides

Electronic-Vibrational Energy Transfer between F-Centers and OH<sup>-</sup> Impurities in Alkali Halides

Electronic-vibrational energy transfer between F centers and OH- impurities in KBr studied by Stokes and anti-Stokes Raman scattering.

Electronic-vibrational energy transfer between F centers and OH- impurities in KBr studied by Stokes and anti-Stokes Raman scattering.

Transient absorption of vibrationally excited FH(CN-) centers in cesium halides: Insight into the electronic-to-vibrational energy transfer.

Pump-and-probe-type experiments covering a wide time range between tens of picoseconds and milliseconds reveal a transient optical absorption of the $F$ center-C${\mathrm{N}}^{\ensuremath{-}}$ defect complex in cesium halides. Its pronounced structure is interpreted in terms of electronic-vibrational transitions of the defect with the C${\mathrm{N}}^{\ensuremath{-}}$ stretching mode highly excited. The detailed analysis shows a substantial change of vibronic energies in the excited electronic state by nonlinear coupling. The measured time for the electron-vibrational energy transfer of about 70 ns in CsBr (and shorter in CsCl) demonstrates that the transfer takes place in the relaxed excited state. We also find that the 10 ms recovery component is due to vibrational relaxation.

Spin coupling and memory effects in the optical cycle of FH centers involving electron-vibrational energy transfer

Spin-coupling and spin memory effects of FH(OH−) and FH(CN-) centers have been studied in various hosts at 2 K. The spin-memory loss ϵ, i.e. the probability of spin-flip during a complete electronic excitation and relaxation cycle, has been determined. The main result is a strong increase of the spin-memory loss ϵ for FH(CN-) in CsCl and CsBr compared to F centers, while ϵ remains nearly unchanged (only a slight decrease) for FH(OH-) centers in KCl and KBr. First attempts will be made to explain these spin-memory loss results in correlation to the electron relaxation and electron-vibrational energy transfer processes occuring in the same optical cycle.

Vibrational fluorescence of CN−centers in KCl by electronic excitation of neighbouring Tl+centers

Abstract Infrared emission from higher vibrational states of CN− in KCl has been achieved by optically exciting nearby Tl+ ions with an excimer laser. The electronic vibrational energy transfer, already known from FH(CN−) in alkali halides, leads to population of vibrational states up to at least the tenth level.

Br*+CO2 revisited: An interrogation of E–V energy transfer with time-resolved diode laser spectroscopy

High resolution (0.0003 cm−1) time-resolved diode laser absorption spectroscopy has been used to reinvestigate the electronic–vibrational energy transfer from spin–orbit excited bromine, Br(2P1/2), to carbon dioxide. The experiments are carried out by generating Br* atoms with pulsed 193 nm laser photolysis of CF3Br and monitoring the subsequent energy transfer by following directly the temporal evolution of selected vibrational states of CO2 (1001, 0201, 0221 and 0001). By comparing the temporal profile of the 1001 state with that predicted by various kinetic models it has been established that quenching of Br* by CO2 occurs via the nearly resonant 1001 state. The E–V rate measured in the present study, (4.8±0.6)×105 Torr−1 s−1, agrees well with that reported previously using infrared fluorescence probes. It has also been determined that the efficiency of this energy transfer is 0.87±0.15; that is, on average, 87% of the spin–orbit excited energy of the Br* atoms will show up as CO2 vibrational energy. The rate constant for the vibrational relaxation of the 1001 state is found to be (4.1±0.5)×106 Torr−1 s−1, also in good agreement with previous low resolution fluorescence measurements.

Stokes and anti-Stokes resonant Raman scattering of FH(CH-) defects in CsBr

Association of F centres with CN- molecular ions in CsBr forms FH(CH-) complexes with electronic absorption bands at 1.78 eV (FH(1)) and 1.94 eV (FH(2)). Using continuous-wave excitation in resonance with these absorptions, the authors studied Stokes and anti-Stokes Raman scattering at low temperature to investigate the F-centre/CN- coupling and the recently observed electronic-vibrational energy transfer by which excited states of the CN- stretching mode become populated. FH(1) and FH(2) excited anti-Stokes spectra show distinct differences in scattered intensity and number of Raman lines, suggesting different coupling strengths and timescales for the corresponding transfer processes. The dependence of the spectra on light polarisation, excitation power and sample temperature is studied and discussed with regard to defect symmetry and relative population of states. The quadratic dependence of scattered intensity on excitation power observed at lowest power level is consistent with a two-step nature of the observed processes, involving population of vibrational states and scattering from these. Owing to the good resolution, the spectra can be analysed in terms of isotope effects on the CN- stretching-mode energy. Preliminary measurements of the lattice phonon and local-mode Raman spectra show that further refinements of the model are required.

Theoretical and experimental study of the quenching of singlet oxygen by solvent

The intermolecular electronic—vibrational energy transfer theory based on dipole—dipole interaction has been extended to treat the quenching of singlet ( 1Δ g) oxygen by solvent. According to this treatment, the off-resonance factor which relates to the singlet oxygen emission bandwidth in the solvent is included in the rate constant expression and has a definite value; the additivity relationship descovered by Schuster and Rodgers can also be explained. The lifetimes of singlet oxygen in n-chloroalkane, n-bromoalkane and n-iodoalkane solvents were determined by measuring the time-resolved decay of singlet oxygen luminescence at 1.27 μm. The excitation source is a laser light which has a pulse width of 15 ns with a maximum power of 7 mJ at 592 nm. A good linear relationship between the bimolecular rate constants and the number of methylene groups in the carbon skeleton of the solvent is found. The bimolecular rate constants contributed by methyl and methylene groups are 250 M −1 s −1 and 800 M −1 s −1 respectively. The finding that the methylene group is a better quencher than the methyl group eliminates the possibility that the highest frequency fundamental vibrational mode plays a more important role than the overtone or the combination mode. The significant increase in the quenching rate constants in iodoalkanes is probably due to an effect other than the heavy atom effect.

Classical model for electronically non-adiabatic collision processes resonance effects in electronic-vibrational energy transfer

A classical model for electronically non-adiabatic collision processes is applied to E → V energy transfer in a collinear system, A + BC ( v = 1) → A ∗ + BC ( v = 0), resembling Br-H 2.The model, which treats electronic as well as translational, rotational, and vibrational degrees of freedom by classical mechanics, describes the resonance features in this process reasonably well.

Electronic to vibrational energy transfer, I( 2P [formula omitted])TO H 2, measured by an optoacoustic technique

An optoacoustic technique is shown to give accurate results for the extent of vibrational excitation in electronic-vibrational energy transfer. The system studied is I( 2P 1 2 )-H 2, and it is shown that within experimental error the transfer is exclusively to the H 2( v″ = 2) vibrational state. Unlike other methods which are dependent on the acceptor molecule showing infrared emission, the technique is of general applicability.