Laser pulse length dependence of internal energy transfer in UV-MALDI-MS

Recent internal energy (IE) measurements for various analytes in matrix-assisted laser desorption ionization (MALDI) have indicated that the amount of IE transferred to analytes not only depends on the matrix but also on the nature of the analyte. Common matrixes, such as -cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SA), and 2,5-dihydroxy-benzoic acid (DHB), had been characterized as cold or hot according to the IEs of analyte ions produced in the corresponding MALDI plume. In this contribution, we present evidence that IE transfer in MALDI depends on the matrix, analyte, as well as on the laser pulse properties. A substituted benzylpyridinium salt as a thermometer molecule (TM) was investigated in CHCA, SA, and DHB matrixes. A nitrogen laser (4 ns pulse length) and a mode locked frequency tripled Nd:YAG laser (22 ps pulse length) were used as excitation sources at various fluences. Survival yields (SYs) of the analyte molecular ions were extracted from the spectra and the corresponding IEs were obtained from Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The SYs indicate that the IEs of analyte ions in MALDI are analyte, matrix, and laser source dependent. The ion generation threshold fluences follow the same order for both lasers: CHCA<SA<DHB, but for the analyte the mode locked 3× Nd:YAG laser source requires a higher threshold fluence than the nitrogen laser. Despite the higher fluence, the SYs are generally higher (the corresponding IEs are lower) for the 3× Nd:YAG laser than for the nitrogen laser. The SYs of the TM molecular ions decrease with an increase of fluence for both the ns laser and the ps laser. PACS 82.80.Ms; 82.20.Nk; 81.15.Fg     

Dynamical correlation between quantum entanglement and intramolecular energy in molecular vibrations:An algebraic approach

The dynamical correlation between quantum entanglement and intramolecular energy in realistic molecular vibrations is explored using the Lie algebraic approach. The explicit expression of entanglement measurement can be achieved using algebraic operations. The common and different characteristics of dynamical entanglement in different molecular vibrations are also provided. The dynamical study of quantum entanglement and intramolecular energy in small molecular vibrations can be helpful for controlling the entanglement and further understanding the intramolecular dynamics.     

Triplet-triplet energy transfer between luminescent probes bound to albumins

The interaction of polar and nonpolar luminescent probes with human blood serum albumins is studied by absorption and luminescence spectroscopy. It is found that the probes (polar eosin and nonpolar anthracene) can efficiently bind to proteins. The radii of the quenching spheres of energy-donor (eosin) triplet states in the presence of an acceptor (anthracene) in the process of the triplet-triplet energy transfer in proteins are determined for homogeneous and inhomogeneous distributions of acceptor molecules over the solution volume. It is shown that a decrease in the radius of the quenching sphere observed upon the addition of sodium dodecylsulfate surfactant is caused by structural changes in the protein.     

Novel aspects of intramolecular electronic energy transfer

Intramolecular electronic energy transfer (intra-EET) was investigated in an isolated bichromophoric naphthalene (N) and anthracene (A) 1:1 molecular cluster. Investigation of the spectroscopic properties of these chromophores, separately and loosely bound in a van der Waals complex, helps to understand the dependence of the EET rate on the initially excited vibronic level and on the cluster’s interchromophoric orientation. A slow intra-EET rate that is associated with an unfavoured orientation of the two chromophores in one of the two possible conformers of the A-N cluster, was observed and was supported by a calculation of the cluster geometry and by comparison with a recent study of intra-EET in the A-(CH₂)_n-N bichromophoric molecules. Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic, 26–30 May 1997. This study was partially supported by grants from the VPR Technion — N. Haar and R. Zinn Research Fund and by the Fund for the Promotion of Research at the Technion.     

Dye lasers and intermolecular and intramolecular energy transfer processes

Computer calculations of ETDL performance indicate that dye laser output can be manipulated by an appropriate choice of a donor (absorber)-acceptor (dye) couple. Studies of relevant laser induced inter- and intramolecular energy transfer processes are presented. Presented in part at the European Physical Society Conference on “Physics and Chemistry of Laser-Induced Processes in Molecules”, Edinburgh (1978) [28].     

Efficiency of intramolecular electronic energy transfer in coumarin bichromophoric molecules

Intramolecular energy transfer in bichromorhoric molecules consisting of two coumarins linked by a variable number of methylene groups (n = 3, 4, 8, 12), was studied with special attention to the effects of n, temperature, viscosity and solvent nature on the efficiency of transfer. The validity of model compounds for the donor and acceptor moieties was carefully examined. Fluorescence polarization experiments revealed that a non-randomicity of mutual orientation of donor and acceptor can only be small, if any. Dual fluorescence from donor and acceptor was observed in propylene glycol whatever the value of n and at any temperature ranging from -60 to 60°C. Fluorescence from the donor was not detectable in dimethylformamide owing to the very low quantum yield of the donor in this solvent. Transfer efficiencies were determined by three steady-state methods and were found to be more dependent on n in dimethylformamide than in propylene glycol. Incomplete energy transfer is clearly shown in the case of dimethylformamide as a solvent. The effects of temperature are weak in the -60, + 60°C range. The results are discussed in light of theories of energy transfer.     

Two-dimensional potential energy function for internal rotation in 1,2-dihydroxybenzenes

We have obtained an analytical expression for the two-dimensional potential energy function for internal rotation in 1,2-dihydroxybenzenes, allowing us to use perturbation theory methods to calculate and interpret the torsional spectra of these compounds. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 133–136, January–February, 2006.     

Determination of the energy levels of total and internal rotation of arbitrary polyatomic molecules with a single internal rotation axis

An algorithm is developed for calculating the eigenvalues of the Hamiltonian operator in the case of asymmetric-asymmetric molecules with a common axis of internal rotation, taking into account the total and internal rotation of these molecules. The algorithm is based on the Ritz variational method. A program is written for reducing a symmetric band matrix to tridiagonal form with subsequent diagonalization of the resulting matrix.State Textile Academy, Ivanovo. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–88, October, 1995.     

Two-photon excited intramolecular energy transfer and light-harvesting effect in novel dendritic systems

Two-photon absorption excited intramolecular energy transfer and light-harvesting effects are demonstrated in three novel dendritic systems. These systems contain both an antenna structure that can effectively absorb two-photon energy at approximately 800 nm and emit fluorescence at approximately 515 nm and a core moiety that can absorb one-photon energy at approximately 520 nm and emit at approximately 590 nm. Covalently combining the core and antenna functionalities intrinsically changes the optical behavior of the component pieces. The two-photon energy absorbed by the antenna structure is resonantly transferred to the core, where the core's emission intensity is enhanced by 8, 20, and 34 times for the three dendritic systems.     

Synthesis,photoluminescence and intramolecular energy transfer model of a dysprosium complex

The energy of the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as their energy gaps, and the singlet and triplet state energy levels of 4-benzoylbenzoic acid (HL=4-BBA) and triphenylphosphine oxide (TPPO) were calculated with the Gaussian03 program package. The singlet state and triplet state energy levels were also estimated from the UV–vis absorption spectra and phosphorescence spectra. The results suggest that the calculated values approximately coincided with the experimental values. A Dy(III) complex was synthesized with 4-BBA as primary ligand and TPPO as neutral ligand. The structure of the complex was characterized by elemental analysis, ¹H NMR spectrometry, and FTIR spectrometry. TG–DTG analysis indicates that the complex kept stable up to 305 °C. The photoluminescence properties were studied by fluorescence spectrometry. The results show that Dy(III) ion sensitized by 4-BBA and TPPO emitted characteristic peaks at 572 nm (⁴F_9/2–⁶H_13/2) and 480 nm (⁴F_9/2–⁶H_15/2), and its Commission Internationale de L'Eclairge coordinates were calculated as x=0.33 and y=0.38, being located in the white range. Intermolecular energy transfer process was discussed and energy transfer model was also proposed.     

Numerical study of energy transfer between a beam and its internal reflection component in a nonlinear medium

A theoretical study is presented of a special case of stationary energy transfer in degenerate two-wave mixing in a reflection geometry. The two interacting beams consist of a beam and its first-order internal reflection component created at the boundary of a nonlinear medium. Numerical results obtained from the computer calculations are presented as graphs. It is found that, under suitable conditions, this phenomenon can be used to eliminate the multiple internal reflections.     

Femtosecond laser control of intramolecular vibrations in a liquid

Optical control of coherent intramolecular oscillations in chloroform CHCl₃ and dimethyl sulfoxide (CH₃)₂SO is attained experimentally under normal conditions by means of femtosecond polarization spectroscopy. Nonresonant excitation of the medium is accomplished by a sequence of two linearly polarized laser pulses. The state of the medium is probed by the third pulse via the optical Kerr effect. We show that control over the vibrational dynamics of molecules on a sub-picosecond scale can be achieved by varying the delay between the excitation pulses and their relative intensity.     

Laser control of intramolecular hydrogen transfer reactions: A real-time path integral approach

Different pulse shapes realizing photo isomerization via laser driven tunnelling or vibrational transitions are studied here. Particular attention is paid to the investigation of their robustness with respect to the influence of dissipative processes introduced by the interaction with an environment. An iterative scheme for propagation of the reduced density matrix in the path integral representation is used to take into account arbitrary system-environment coupling strengths as well as the effect of non-Markovian dynamics.     

Collision-induced rovibrational energy transfer in small polyatomic molecules: the role of intramolecular perturbations

ABSTRACT

Various forms of time-resolved optical double-resonance spectroscopy facilitate rotationally resolved measurements of collision-induced intramolecular vibration-to-vibration (V–V) energy-transfer processes, which take a gas-phase polyatomic molecule from one distinct rovibrational energy level to another. Of longstanding mechanistic interest are questions concerning the extent to which such V–V energy transfer (ET) may be influenced by intramolecular perturbations – notably Fermi resonance (and other anharmonic mixing effects) and Coriolis coupling – within polyatomic molecular rovibrational manifolds of interest. It is evident that quantum-mechanical interference effects can arise, either inhibiting or enhancing the probability of collision-induced ET in perturbed rovibrational manifolds of certain small gas-phase polyatomic molecules, notably CO₂, D₂CO and C₂H₂. This article focuses on a blend of high-resolution rovibrational spectroscopy (characterising initial and final molecular levels and their intramolecular perturbations) and collision dynamics (with colliding molecules defined in terms of isolated-molecule spectroscopic basis states). It aims to offer fresh insights and to consider some apparent mechanistic anomalies (e.g. collision-induced quasi-continuous background effects in the 4ν_CH rovibrational manifold of C₂H₂). Various reported experiments and related theoretical treatments are critically re-examined, in order to pose and address mechanistic questions some of which still challenge detailed understanding.     

Laser induced collisional energy transfer processes in a rubidium-potassium mixture

Two laser induced collisional energy transfer processes in alkali vapours are investigated. For process K(4²S_1/2)+ Rb(5²P_3/2)+?ω_T→K(6²S_1/2)+Rb(5²S_1/2), a population inversion between the final state K(6²S_1/2) and lower states, leading to a superradiant emission has been observed. Comparison between experiment and theory shows a qualitative agreement in the limit of low atomic densities and laser power. However the transfer profile width is about two times larger than the calculated one for both processes.     

Perturbations in the vibration-rotation-torsion energy levels of an ethane molecule exhibiting internal rotation splittings

Various examples of perturbations in the vibration-rotation-torsion energy levels of an ethane molecule exhibiting internal rotation splittings are discussed, both from the point of view of the point group D_3d, appropriate when internal rotation tunneling effects cannot be observed, and from the point of view of the group $\text{G}{}_{36}{}^2$, appropriate when internal rotation tunneling in ethane leads to observable splittings in the spectrum. It is found, for perturbations allowed in both D_3d and $\text{G}{}_{36}{}^2$, that each of the two torsional components of the perturbed D_3d vibration-rotation level can in principle interact with a “corresponding” torsional component in the perturbing vibration-rotation level. It is found for perturbations forbidden in D_3d but allowed in $\text{G}{}_{36}{}^2$, which all occur between D_3d vibrational levels of different g, u parity, that only one of the two torsional components of the perturbed D_3d vibration-rotation level can interact with a corresponding torsional component in the perturbing vibration-rotation level. Some of the perturbations examined give intensity to otherwise forbidden transitions in such a way that perturbation-induced transitions can be used in conjunction with normally allowed transitions to determine the sum of the internal rotation splittings for two rotational levels differing in K by three units.     

Laser conferral of a directed character to near-field energy transfer

With sufficient intensity, an off-resonant laser beam can modify the character of electromagnetic near-field radiation produced by a nanoscale point source, narrowing its spatial distribution. The mechanism, for which the laser frequency is significantly off-resonant from the emission radiation, is detailed and analyzed through a quantum electrodynamical analysis. Results are calculated for various positions of a polarization-sensitive probe relative to the point source, sited within the throughput beam, and contour maps exhibit variations in the registered signal over a range of input intensities. A key feature is the clear exhibition of directed propagation features, usually emergent only in the wave zone, within the near-field region of the source.     

Influence of intramolecular vibrations in charge redistribution at the pentacene-graphite interface

We have investigated the relation between the intramolecular vibrational modes of pentacene and the charge redistribution at the pentacene-graphite interface by using high-resolution electron-energy-loss-spectroscopy. The three main vibrational peaks shift to lower energies as the pentacene film thickness decreases. In order to discuss this energy shift, we have calculated the vibrational energies of a free pentacene molecule by changing its charge state. We have also calculated the vibrational energies of a pentacene molecule adsorbed on a graphite sheet by changing the pentacene-graphite distance. Taking the experimental and calculation results into account, we conclude that the observed energy shifts result from an intramolecular charge redistribution. The present results indicate that the effect of an intramolecular charge redistribution is essential to discuss the origin of an energy shift observed in a vibrational study of an organic molecule/substrate interface.