Excited-State Dipole Moments and Transition Dipole Orientations of Rotamers of 1,2-, 1,3-, and 1,4-Dimethoxybenzene.

Rotationally resolved electronic Stark spectra of rotamers of 1,2-, 1,3-, and 1,4-dimethoxybenzene have been recorded and analyzed using evolutionary strategies. The experimentally determined dipole moments as well as the transition dipole moments are compared to the results of ab initio calculations. For the electronic ground states of the experimentally observed dimethoxybenzenes, the permanent dipole moments can be obtained from vectorial addition of the monomethoxybenzene dipole moment.

Rotationally resolved electronic spectroscopy of the rotamers of 1,3-dimethoxybenzene.

Conformational assignments in molecular beam experiments are often based on relative energies, although there are many other relevant parameters, such as conformer-dependent oscillator strengths, Franck-Condon factors, quantum yields and vibronic couplings. In the present contribution, we investigate the conformational landscape of 1,3-dimethoxybenzene using a combination of rotationally resolved electronic spectroscopy and high level ab initio calculations. The electronic origin of one of the three possible planar rotamers (rotamer (0,180) with both substituents pointing at each other) has not been found.

Ultrafast kinetics of linkage isomerism in Na[Fe(CN)NO] aqueous solution revealed by time-resolved photoelectron spectroscopy.

The kinetics of ultrafast photoinduced structural changes in linkage isomers is investigated using Na[Fe(CN)NO] as a model complex. The buildup of the metastable side-on configuration of the NO ligand, as well as the electronic energy levels of ground, excited, and metastable states, has been revealed by means of time-resolved extreme UV (XUV) photoelectron spectroscopy in aqueous solution, aided by theoretical calculations. Evidence of a short-lived intermediate state in the isomerization process and its nature are discussed, finding that the complete isomerization process occurs in less than 240 fs after photoexcitation.

Modulation of the L/L Mixing in an Indole Derivative: A Position-Dependent Study Using 4-, 5-, and 6-Fluoroindole.

The lowest two electronically excited singlet states of indole and its derivatives are labeled as L or L, based on the orientation of the transition dipole moment (TDM) and the magnitude of the permanent electric dipole moment. Rotationally resolved electronic Stark spectroscopy in combination with high level ab initio calculations offers the possibility to determine these characteristics and thus the electronic nature of the excited states. In the present contribution this approach was pursued for the systems 4- and 6-fluoroindole and the results compared to the previously investigated system 5-fluoroindole.

Ultrafast Spin Crossover in [Fe (bpy) ] : Revealing Two Competing Mechanisms by Extreme Ultraviolet Photoemission Spectroscopy.

Photoinduced spin-flip in Fe complexes is an ultrafast phenomenon that has the potential to become an alternative to conventional processing and magnetic storage of information. Following the initial excitation by visible light into the singlet metal-to-ligand charge-transfer state, the electronic transition to the high-spin quintet state may undergo different pathways. Here we apply ultrafast XUV (extreme ultraviolet) photoemission spectroscopy to track the low-to-high spin dynamics in the aqueous iron tris-bipyridine complex, [Fe(bpy) ] , by monitoring the transient electron density distribution among excited states with femtosecond time resolution.

Ultrafast excited states dynamics of [Ru(bpy)] dissolved in ionic liquids.

Room-temperature ionic liquids (ILs) represent a well-known class of materials exhibiting extremely low vapor pressures and high electrochemical stability. These properties make ILs attractive for various applications requiring UHV conditions. Here, we apply 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][TfO] as a solvent to investigate the excited state dynamics of the transition metal complex [Ru(bpy)] with the use of ultrafast XUV photoelectron spectroscopy.

On the Additivity of Molecular Fragment Dipole Moments of 5-Substituted Indole Derivatives.

The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, particularly for electronically excited states. Herein, we find rules for a number of indole derivatives by using rotationally resolved electronic Stark spectroscopy and ab initio calculations.

The conformational space of the neurotransmitter serotonin: how the rotation of a hydroxyl group changes all.

The 5-hydroxytryptamine receptors (5HTn) are optimized for 5-hydrotryptamine molecules, resulting in a significantly enhanced psychoactive response compared with the 4-, 6-, 7-isomers. This is despite their relatively similar energetic stabilities, excited state lifetimes and emission characteristics. In this work we investigate the conformational space of serotonin (5-hydroxytryptamine) using a combination of rotationally resolved electronic spectroscopy and ab initio calculations.

Charge Transfer Dynamics at Dye-Sensitized ZnO and TiO2 Interfaces Studied by Ultrafast XUV Photoelectron Spectroscopy.

Interfacial charge transfer from photoexcited ruthenium-based N3 dye molecules into ZnO thin films received controversial interpretations. To identify the physical origin for the delayed electron transfer in ZnO compared to TiO2, we probe directly the electronic structure at both dye-semiconductor interfaces by applying ultrafast XUV photoemission spectroscopy. In the range of pump-probe time delays between 0.

Electronic spectra of 2- and 3-tolunitrile in the gas phase. I. A study of methyl group internal rotation via rovibronically resolved spectroscopy.

Rotationally resolved fluorescence excitation spectra of the origin bands in the S1 ← S0 transition of 2-tolunitrile (2TN) and 3-tolunitrile (3TN) have been recorded in the collision-free environment of a molecular beam. Analyses of these data provide the rotational constants of each molecule and the potential energy curves governing the internal rotation of the attached methyl groups in both electronic states. 2TN exhibits much larger barriers along this coordinate than 3TN.

Determination of ground and excited state dipole moments via electronic Stark spectroscopy: 5-methoxyindole.

The dipole moments of the ground and lowest electronically excited singlet state of 5-methoxyindole have been determined by means of optical Stark spectroscopy in a molecular beam. The resulting spectra arise from a superposition of different field configurations, one with the static electric field almost parallel to the polarization of the exciting laser radiation, the other nearly perpendicular. Each field configuration leads to different intensities in the rovibronic spectrum.

Charge transfer to solvent dynamics in iodide aqueous solution studied at ionization threshold.

We explore the early-time electronic relaxation in NaI aqueous solution exposed to a short UV laser pulse. Rather than initiating the charge transfer reaction by resonant photoexcitation of iodide, in the present time-resolved photoelectron spectroscopy study the charge-transfer-to-solvent (CTTS) states are populated via electronic excitation above the vacuum level. By analyzing the temporal evolution of electron yields from ionization of two transient species, assigned to CTTS and its first excited state, we determine both their ultrafast population and relaxation dynamics.

Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates.

We report on a newly built laser-based tabletop setup which enables generation of femtosecond light pulses in the XUV range employing the process of high-order harmonic generation (HHG) in a gas medium. The spatial, spectral, and temporal characteristics of the XUV beam are presented. Monochromatization of XUV light with minimum temporal pulse distortion is the central issue of this work.

High resolution electronic spectroscopy of vibrationally hot bands of benzimidazole.

Rotationally resolved electronic spectra of seven vibrationally excited bands in the electronic spectrum of benzimidazole have been measured and analyzed. From the vibrational contributions to the rotational constants, an assignment of the hot bands could be made on the basis of anharmonic corrections to the harmonic normal modes and by using the information contained in the Duschinsky matrix calculated by second order coupled cluster (CC2) theory. Fluorescence emission and (hot) absorption spectra of benzimidazole from Jalviste and Treshchalov [Chem.

Time-of-flight electron spectrometer for a broad range of kinetic energies.

A newly constructed time-of-flight electron spectrometer of the magnetic bottle type is characterized for electron detection in a broad range of kinetic energies. The instrument is designed to measure the energy spectra of electrons generated from liquids excited by strong laser fields and photons in the range of extreme ultra violet and soft X-rays. Argon inner shell electrons were recorded to calibrate the spectrometer and investigate its characteristics, such as energy resolution and collection efficiency.

Position matters: high resolution spectroscopy of 6-methoxyindole.

The structures of syn and anti 6-methoxyindole have been determined in the electronic ground and excited states using rotationally resolved electronic spectroscopy and high level ab initio calculations. Second order coupled cluster theory predicts the lowest excited singlet states to be heavily mixed and the transition dipole moments to depend strongly on the geometries. From the analysis of the rovibronic spectra of seven isotopomers, the absolute orientation of the transition dipole moment within the principle axis frame was determined to be L(b)-like for both conformers.

Ground and electronically excited singlet state structures of the syn and anti rotamers of 5-hydroxyindole.

The electronic origin bands A and B of 5-hydroxyindole were measured using rotationally resolved electronic spectroscopy. From comparison of the experimental rotational constants to the results of ab initio calculated structures, we could make the assignment of band A being due to the syn conformer and of band B being due to the anti conformer. These conformers, which differ in the orientation of the hydroxy group with respect to the rest of the molecule, have considerably different S1 state life times.

Ground and electronically excited singlet-state structures of 5-fluoroindole deduced from rotationally resolved electronic spectroscopy and ab initio theory.

The structure and electronic properties of the electronic ground state and the lowest excited singlet state (S(1)) of 5-fluoroindole (5FI) were determined by using rotationally resolved spectroscopy of the vibration-less electronic origin of 5FI. From the parameters of the axis reorientation Hamiltonian, the absolute orientation of the transition dipole moment in the molecular frame was determined and the character of the excited state was identified as L(b).