Directional Dynamics in the Photodissociation of Oriented Molecules

Resonance-state selective photodissociation dynamics of OCS + hv → CS(X1Σ+) + O(3Pj=2,1,0) via the 21Σ+ state

Understanding vacuum ultraviolet photodissociation dynamics of Carbonyl sulfide (OCS) is of considerable importance in the study of atmospheric chemistry. Yet, photodissociation dynamics of the CS(X1Σ+) + O(3Pj=2,1,0) channels following excitation to the 21Σ+(ν1',1,0) state has not been clearly understood so far. Here, we investigate the O(3Pj=2,1,0) elimination dissociation processes in the resonance-state selective photodissociation of OCS between 147.24 and 156.48 nm by using the time-sliced velocity-mapped ion imaging technique. The total kinetic energy release spectra are found to exhibit highly structured profiles, indicative of the formation of a broad range of vibrational states of CS(1Σ+). The fitted CS(1Σ+) vibrational state distributions differ for the three 3Pj spin-orbit states, but a general trend of the inverted characteristics is observed. Additionally, the wavelength-dependent behaviors are also observed in the vibrational populations for CS(1Σ+, v). The CS(X1Σ+, v = 0) has a significantly strong population at several shorter wavelengths, and the most populated CS(X1Σ+, v) is gradually transferred to a higher vibrational state with the decrease in the photolysis wavelength. The measured overall β-values for the three 3Pj spin-orbit channels slightly increase and then abruptly decrease as the photolysis wavelength increases, while the vibrational dependences of β-values show an irregularly decreasing trend with increasing CS(1Σ+) vibrational excitation at all studied photolysis wavelengths. The comparison of the experimental observations for this titled channel and the S(3Pj) channel reveals that two different intersystem crossing mechanisms may be involved in the formation of the CS(X1Σ+) + O(3Pj=2,1,0) photoproducts via the 21Σ+ state.

Orientation of Chiral Molecules by External Electric Fields: Focus on Photodissociation Dynamics

Molecular orientation is a fundamental requirement to study and control photoinitiated reactions. Experimental setups that make use of hexapolar electric filters combined with slice-ion imaging detectors were employed in these last years to investigate the photodissociation dynamics of chiral molecules. The final goal is the on-the-fly discrimination of oriented enantiomers, revealed by the different angular distributions in photofragment ion-imaging, as predicted from vector correlation studies. Here, we review experiments of photodissociation of oriented chiral molecules, with the aim of presenting limits emerging from these investigations and perspectives toward the achievement of the ultimate objective.

Conformer Selection by Electrostatic Hexapoles: A Theoretical Study on 1-Chloroethanol and 2-Chloroethanol

The electrostatic hexapole is a versatile device that has been used for many years in gas-phase experiments. Its inhomogeneous electric field has been employed for many purposes such as the selection of rotational states, the selection of clusters, the focusing of molecular beams, and molecular alignment as a precursor for molecular orientation. In the last few years, the hexapolar electric field has been demonstrated to be able to control the conformer composition of molecular beams. The key point is that conformers, where the component of the permanent electric dipole moment with respect to the largest of the principal axes of inertia is close to zero, require more intense hexapolar electric fields to be focused with respect to the other conformers. Here, we simulated the focusing curves of the conformers of 1-chloroethanol and 2-chloroethanol under hypothetical beam conditions, identical for all conformers, in a hypothetical and realistic experimental setup with three different hexapole lengths: 0.5, 1, and 2 m. The objective was to characterize this selection process to set up collision experiments on conformer-selected beams that provide information on the van der Waals clusters formed in collision processes.

Time-resolving the UV-initiated photodissociation dynamics of OCS

We present a time-resolved study of the photodissociation dynamics of OCS after UV-photoexcitation at λ = 237 nm. OCS molecules (X1Σ+) were primarily excited to the 11A'' and the 21A' Renner-Teller components of the 1Σ- and 1Δ states. Dissociation into CO and S fragments was observed through time-delayed strong-field ionisation and imaging of the kinetic energy of the resulting CO+ and S+ fragments by intense 790 nm laser pulses. Surprisingly, fast oscillations with a period of ∼100 fs were observed in the S+ channel of the UV dissociation. Based on wavepacket-dynamics simulations coupled with a simple electrostatic-interaction model, these oscillations do not correspond to the known highly-excited rotational motion of the leaving CO(X1Σ+, J ≫ 0) fragments, which has a timescale of ∼140 fs. Instead, we suggest to assign the observed oscillations to the excitation of vibrational wavepackets in the 23A'' or 21A'' states of the molecule that predissociate to form S(3PJ) photoproducts.

Vacuum ultraviolet photodissociation dynamics of OCS + hv → CO(1Σ+) + S(1S0) via the E and F Rydberg states

The state-resolved photodissociation of the CO(1Σ+) + S(1S0) photoproduct channel, formed by vacuum ultraviolet photoexcitation of OCS to a progression of the symmetric stretching vibration (ν1') in the E and F states, has been investigated by using the time-sliced velocity map ion imaging technique. The total kinetic energy release spectra and the vibrational state specific anisotropy parameters (β) were obtained based on the raw images of S(1S0) photoproducts detected in the wavelength ranges of 134.40-140.98 nm, respectively. Except for vibrational band origins, the CO(1Σ+) photoproducts are found to have more significant populations at highly vibrationally excited states as the symmetric stretching vibrational excitation of the E and F states increases. Furthermore, the vibrational-state specific β values for the CO(1Σ+) + S(1S0) channel via the E and F states both show a sudden change from negative to positive in the vicinity of moderately vibronic levels of the E and F states. This anomalous phenomenon suggests that multiple excited states with different symmetries are involved in the photoexcitation process at relatively short photolysis wavelengths due to the strong vibronic couplings existing in the higher vibronic levels of the E and F states, and the formation of CO(1Σ+) + S(1S0) photoproducts may proceed by different nonadiabatic interactions from the prepared excited states to the lower dissociative state 1Σ+, with strong dependence of the initially symmetric stretching excitation in the Rydberg-type transitions.

Photodissociation Dynamics of OCS near 150 nm: The S(1SJ=0) and S(3PJ=2,1,0) Product Channels

Vacuum ultraviolet photodissociation dynamics of carbonyl sulfide (OCS) was investigated by using the time-sliced velocity map ion imaging technique. Images of the S(¹S_J=0) and S(³P_J=2,1,0) photofragments formed in the OCS photodissociation were acquired at six photolysis wavelengths from 147.24 to 156.48 nm. Vibrational states of the CO coproducts were partially resolved and identified in the images. Two main dissociation product channels, namely, the spin-allowed S(¹S_J=0) + CO(X¹Σ_g⁺) and spin-forbidden S(³P_J=2,1,0) + CO(X¹Σ_g⁺), were observed. At each photolysis wavelength, the total kinetic energy releases, the relative population of different CO vibrational states, and the anisotropic parameters were derived. Variations of the relative population were noticed between different spin-orbit states of the S(³P_J) channel. It was found that the S(¹S_J=0) + CO(X¹Σ_g⁺) channel is dominated by the ¹Σ⁺ ← ¹Σ⁺ parallel transition of OCS. Interestingly, two types of anisotropic parameters are found at different photolysis wavelengths for the spin-forbidden S(³P_J=2,1,0) + CO(X¹Σ_g⁺) product channel. The anisotropic parameters at 147.24 and 150.70 nm are significantly smaller than at the other four photolysis wavelengths. This phenomenon indicates two different nonadiabatic pathways are responsible for the spin-forbidden channels, which is consistent with the barrier structure in the exit channel of one of the triplet states.

Laser-induced dynamics of molecules with strong nuclear quadrupole coupling

We present a general variational approach for computing the laser-induced rovibrational dynamics of molecules, taking into account the hyperfine effects of the nuclear quadrupole coupling. The method combines the general variational approach TROVE (Theoretical Ro-Vibrational Energies), which provides accurate rovibrational hyperfine energies and wavefunctions for arbitrary molecules, with the variational method RichMol, designed for generalized simulations of the rovibrational dynamics in the presence of external electric fields. We investigate the effect of the nuclear quadrupole coupling on the short-pulse laser alignment of a prototypical molecule CFClBrI, which contains nuclei with large quadrupole constants. The influence of the nuclear quadrupole interactions on the postpulse molecular dynamics is negligible at early times, for the first several revivals; however, at longer time scales, the effect is entirely detrimental and strongly depends on the laser intensity. This effect can be explained by dephasing in the laser-excited rotational wavepacket due to irregular spacings between the hyperfine-split nuclear spin states across different rotational hyperfine bands.

Observation of the Carbon Elimination Channel in Vacuum Ultraviolet Photodissociation of OCS

The textbook mechanism for OCS photodissociation mainly involves the CO + S or CS + O product channel via a single bond fission. However, a third dissociation channel concerning the cleavage of both C-S and C-O bonds yielding SO + C products, though thermodynamically allowed, has never been verified experimentally to date. By using a tunable vacuum ultraviolet laser light and time-sliced velocity map ion imaging technique, we have clearly observed the SO(X³Σ^-) + C(³P_J=0) products as the vacuum ultraviolet laser photon energy gradually exceeds its thermodynamic threshold. The corresponding SO(X³Σ^-) coproducts are highly vibrationally excited and show varying angular distributions from isotropic to anisotropic as the excitation photon energy increases. Theoretical analysis suggests that a fast nonadiabatic pathway plays a dominant role in the formation of the anisotropic SO products. That isotropic products arise as the excitation photon energies approach the thermodynamic threshold can be reasonably explained by the "roaming mechanism".

Stereodynamic Imaging of Bromine Atomic Photofragments Eliminated from 1-Bromo-2-methylbutane Oriented via Hexapole State Selector

Both single-laser and two-laser experiments were conducted to look into the ion-imaging of Br*(²P_1/2) and Br(²P_3/2) photofragmented from 1-bromo-2-methylbutane in the range 232-240 nm via a detection scheme of (2+1) resonance-enhanced multiphoton ionization. The angular analysis of these photofragment distributions yields the anisotropy parameter β = 1.88 ± 0.06 for the Br* excited state which arises from a parallel transition, while β = 0.63 ± 0.09 for the Br ground state indicates the contribution from both a perpendicular transition and a non-adiabatic transition. When a hexapole coupled with an orienting field was implemented, the parent molecules are spatially oriented to yield an orientation efficiency |⟨cos θ⟩| of 0.15. Besides the χ angle between the recoil velocity v and the transition dipole moment μ, orienting molecules allows for the evaluation of the angle α between v and the permanent molecular dipole moment d. The angular analysis of Br* photofragment distribution yields χ = 11.5° and α in the range from 160° to 180° with weak dependency. In the two-laser experiments, the angular anisotropy of Br photofragment distribution was found to be smaller (0.38 ± 0.10) when the photolysis wavelength was red-shifted to 240 nm, suggesting the increasing contributions from perpendicular transitions.

Molecular movie of ultrafast coherent rotational dynamics of OCS

Recording molecular movies on ultrafast timescales has been a longstanding goal for unravelling detailed information about molecular dynamics. Here we present the direct experimental recording of very-high-resolution and -fidelity molecular movies over more than one-and-a-half periods of the laser-induced rotational dynamics of carbonylsulfide (OCS) molecules. Utilising the combination of single quantum-state selection and an optimised two-pulse sequence to create a tailored rotational wavepacket, an unprecedented degree of field-free alignment, 〈cos2θ2D〉 = 0.96 (〈cos2θ〉 = 0.94) is achieved, exceeding the theoretical limit for single-pulse alignment. The very rich experimentally observed quantum dynamics is fully recovered by the angular probability distribution obtained from solutions of the time-dependent Schrödinger equation with parameters refined against the experiment. The populations and phases of rotational states in the retrieved time-dependent three-dimensional wavepacket rationalises the observed very high degree of alignment.

Vectorial imaging of the photodissociation of 2-bromobutane oriented via hexapolar state selection

Molecular orientation techniques are becoming available in the study of elementary chemical processes, in order to highlight those structural and dynamical properties that would be concealed by random rotational motions. Recently successful orientation was achieved for asymmetric-top and chiral molecules of much larger complexity than hitherto. In this work, we report and discuss the correlation between the vectors' photofragment recoil velocity v, transition dipole moment μ, and permanent dipole moment d in a dissociation experiment on hexapole oriented 2-bromobutane, photoinitiated by a linearly polarized laser. The sliced ion images of the Br*(2P1/2) and Br(2P3/2) photofragments were acquired at 234.0 and 254.1 nm, respectively, by a (2 + 1) resonance-enhanced multiphoton ionization technique. A detailed analysis of the sliced ion images obtained at a tilting angle 45° of laser polarization provides information on the correlation of the three vectors, which are confined by two polar angles α and χ and one azimuthal angle φμd in the recoil frame. The sliced ion images of Br fragments eliminated individually from the enantiomers at 254.1 nm yield an asymmetric factor close to zero; for this reason the photofragment angular distributions do not show significant differences. The elimination of the Br* fragment at 234.0 nm is mainly correlated with a parallel transition, giving rise to a large anisotropy parameter of 1.85, and thus can be considered as a single state excitation. The resulting recoil frame angles are optimized to 163° ± 8° and 164° ± 1° for α and χ, respectively, whereas φμd is approaching 0° for the best fit. Since for the present molecule, the three vectors have an only slight spatial arrangement, the photofragment angular distributions of the two enantiomers do not show appreciable differences. Theoretical and computational simulations provide us the basis to state that oriented enantiomers can be discriminated on-the-fly in photodissociation processes even initiated by non-circularly polarized light, provided that the three vectors encountered above have specific three-dimensional arrangements. The fact that Br fragment elimination involves a multi-potential dissociation carries uncertainties in theoretical estimates of the vector direction. Therefore, this work represents a preliminary but significant step on the road to chiral discrimination on-the-fly, which is shown to be best propitiated in molecules where vectors are far from having degenerate mutual angular directions.

Quantum optimal control of multiple weakly interacting molecular rotors in the time-dependent Hartree approximation

We perform quantum optimal control simulations, based on the Time-Dependent Hartree (TDH) approximation, for systems of three to five dipole-dipole coupled OCS rotors. A control electric field is used to steer all of the individual rotors, arranged in chains and regular polygons in a plane, toward either identical or unique objectives. The goal is to explore the utility of the TDH approximation to model the field-induced dynamics of multiple interacting rotors in the weak dipole-dipole coupling regime. A stochastic hill climbing approach is employed to seek an optimal control field that achieves the desired objectives at a specified target time. We first show that multiple rotors in chain and polygon geometries can be identically oriented in the same direction; these cases do not significantly depend on the presence of the dipole-dipole interaction. Additionally, in particular geometrical arrangements, we demonstrate that individual rotors can be uniquely manipulated toward different objectives with the same field. Specifically, it is shown that for a three rotor chain, the two end rotors can be identically oriented in a specific direction while keeping the middle rotor in its ground state, and for an equilateral triangle, two rotors can be identically oriented in a specific direction while the third rotor is oriented in the opposite direction. These multirotor unique objective cases exploit the shape of the field in coordination with dipole-dipole coupling between the rotors. Comparisons to numerically exact calculations, utilizing the TDH-determined fields, are given for all optimal control studies involving systems of three rotors.

Determining Orientations of Optical Transition Dipole Moments Using Ultrafast X-ray Scattering

Identification of the initially prepared, optically active state remains a challenging problem in many studies of ultrafast photoinduced processes. We show that the initially excited electronic state can be determined using the anisotropic component of ultrafast time-resolved X-ray scattering signals. The concept is demonstrated using the time-dependent X-ray scattering of N-methyl morpholine in the gas phase upon excitation by a 200 nm linearly polarized optical pulse. Analysis of the angular dependence of the scattering signal near time zero renders the orientation of the transition dipole moment in the molecular frame and identifies the initially excited state as the 3p _z Rydberg state, thus bypassing the need for further experimental studies to determine the starting point of the photoinduced dynamics and clarifying inconsistent computational results.

Time-dependent analysis of the mixed-field orientation of molecules without rotational symmetry

We present a theoretical study of the mixed-field orientation of molecules without rotational symmetry. The time-dependent one-dimensional and three-dimensional orientation of a thermal ensemble of 6-chloropyridazine-3-carbonitrile molecules in combined linearly or elliptically polarized laser fields and tilted dc electric fields is computed. The results are in good agreement with recent experimental results of one-dimensional orientation for weak dc electric fields [J. L. Hansen, J. Chem. Phys. 139, 234313 (2013)]. Moreover, they predict that using elliptically polarized laser fields or strong dc fields, three-dimensional orientation is obtained. The field-dressed dynamics of excited rotational states is characterized by highly non-adiabatic effects. We analyze the sources of these non-adiabatic effects and investigate their impact on the mixed-field orientation for different field configurations in mixed-field-orientation experiments.

Strong laser field control of fragment spatial distributions from a photodissociation reaction

The notion that strong laser light can intervene and modify the dynamical processes of matter has been demonstrated and exploited both in gas and condensed phases. The central objective of laser control schemes has been the modification of branching ratios in chemical processes, under the philosophy that conveniently tailored light can steer the dynamics of a chemical mechanism towards desired targets. Less explored is the role that strong laser control can play on chemical stereodynamics, i.e. the angular distribution of the products of a chemical reaction in space. This work demonstrates for the case of methyl iodide that when a molecular bond breaking process takes place in the presence of an intense infrared laser field, its stereodynamics is profoundly affected, and that the intensity of this laser field can be used as an external knob to control it.

Recoil Inversion in the Photodissociation of Carbonyl Sulfide near 234 nm

We report the observation of recoil inversion of the CO (v=0, J_{CO}=66) state in the UV dissociation of lab-frame oriented carbonyl sulfide (OCS). This state is ejected in the opposite direction with respect to all other (>30) states and in absence of any OCS rotation, thus resulting in spatial filtering of this particular high-J rovibrational state. This inversion is caused by resonances occurring in shallow local minima of the molecular potential, which bring the sulfur closer to the oxygen than the carbon atom, and is a striking example where such subtleties severely modify the photofragment trajectories. The resonant behavior is observed only in the photofragment trajectories and not in their population, showing that stereodynamic measurements from oriented molecules offer an indispensable probe for exploring energy landscapes.

Impulsive laser-induced alignment of OCS molecules at FERMI

OCS full rotational revival dynamics induced by impulsive NIR alignment monitored by Coulomb explosion correlated fragments after S 2p excitation.

On the state selection of linear triatomic molecules by electrostatic hexapole fields

Electrostatic hexapole state-selector is a versatile tool in experimental stereodynamics. The requirement of appropriate models to correctly predict the behavior of molecules in the hexapole motivated us to realize a treatment that predicts the Stark effect of linear triatomic molecules with rotational doublet states. Various perturbative approximations are conventionally adopted to obtain analytic Stark energy derivatives of a truncated Hamiltonian matrix, without utilizing numerical diagonalization of the full Hamiltonian matrix. By including both the low and high field effects, which were alternatively ignored in the analytical formulae of such approximate approaches, herein we demonstrate that the performance of hexapole state selector to linear triatomic molecules can be appropriately predicted via Van Vleck transformation. This method can provide analytic Stark energy derivatives that are acceptably in consistent with the ones obtained via numerical diagonalization of the full Hamiltonian matrix. Particularly, this work is suitable for v2 = 1 level of linear triatomic molecules, due to the following reasons: (1) the Stark energy derivative and the molecular orientation as a function of the electric field are expressed in analytical formulae, hence it is suitable for implementation without involving numerical diagonalization of the full Hamiltonian matrix; (2) a better prediction of the focusing curves with respect to conventional analytical treatments is provided, allowing a reliable determination of the selected state compositions and molecular orientation.

Hexapole-Oriented Asymmetric-Top Molecules and Their Stereodirectional Photodissociation Dynamics

Molecular orientation is a fundamental requisite in the study of stereodirected dynamics of collisional and photoinitiated processes. In this past decade, variable hexapolar electric filters have been developed and employed for the rotational-state selection and the alignment of molecules of increasing complexity, for which the main difficulties are their mass, their low symmetry, and the very dense rotational manifold. In this work, for the first time, a complex molecule such as 2-bromobutane, an asymmetric top containing a heavy atom (the bromine), was successfully oriented by a weak homogeneous field placed downstream from the hexapolar filter. Efficiency of the orientation was characterized experimentally, by combining time-of-flight measurements and a slice-ion-imaging detection technique. The application is described to the photodissociation dynamics of the oriented 2-bromobutane, which was carried out at a laser wavelength of 234 nm, corresponding to the breaking of the C-Br bond. The Br photofragment is produced in both the ground Br ((2)P3/2) and the excited Br ((2)P1/2) electronic states, and both channels are studied by the slice imaging technique, revealing new features in the velocity and angular distributions with respect to previous investigations on nonoriented molecules.

Laser induced alignment of state-selected CH3I

Hexapole state selection is used to prepare CH3I molecules in the |JKM〉 = |1±1∓1〉 state. The molecules are aligned in a strong 800 nm laser field, which is linearly polarised perpendicular to the weak static extraction field E of the time of flight setup. The molecules are subsequently ionised by a second time delayed probe laser pulse. It will be shown that in this geometry at high enough laser intensities the Newton sphere has sufficient symmetry to apply the inverse Abel transformation to reconstruct the three dimensional distribution from the projected ion image. The laser induced controllable alignment was found to have the upper and lower extreme values of 〈P2(cos θ)〉 = 0.7 for the aligned molecule and -0.1 for the anti-aligned molecule, coupled to 〈P4(cos θ)〉 between 0.3 and 0.0. The method to extract the alignment parameters 〈P2(cos θ)〉 and 〈P4(cos θ)〉 directly from the velocity map ion images will be discussed.

Two-state wave packet for strong field-free molecular orientation

We demonstrate strong laser-field-free orientation of absolute-ground-state carbonyl sulfide molecules. The molecules are oriented by the combination of a 485-ps-long nonresonant laser pulse and a weak static electric field. The edges of the laser pulse create a coherent superposition of two rotational states resulting in revivals of strong transient molecular orientation after the laser pulse. The experimentally attained degree of orientation ⟨cosθ⟩≈0.6 corresponds to the theoretical maximum for mixing of the two states. Switching off the dc field would provide the same orientation completely field free.

Two-pulse field-free orientation reveals anisotropy of molecular shape resonance

We report the observation of macroscopic field-free orientation, i.e., more than 73% of CO molecules pointing in the same direction. This is achieved through an all-optical scheme operating at high particle densities (>10(17)  cm(-3)) that combines one-color (ω) and two-color (ω+2ω) nonresonant femtosecond laser pulses. We show that the achieved orientation solely relies on the hyperpolarizability interaction as opposed to an ionization-depletion mechanism, thus, opening a wide range of applications. The achieved strong orientation enables us to reveal the molecular-frame anisotropies of the photorecombination amplitudes and phases caused by a shape resonance. The resonance appears as a local maximum in the even-harmonic emission around 28 eV. In contrast, the odd-harmonic emission is suppressed in this spectral region through the combined effects of an asymmetric photorecombination phase and a subcycle Stark effect, generic for polar molecules, that we experimentally identify.

High-harmonic spectroscopy of oriented OCS molecules: emission of even and odd harmonics

We study the emission of even and odd high-harmonic orders from oriented OCS molecules. We use an intense, nonresonant femtosecond laser pulse superimposed with its phase-controlled second harmonic field to impulsively align and orient a dense sample of molecules from which we subsequently generate high-order harmonics. The even harmonics appear around the full revivals of the rotational dynamics. We demonstrate perfect coherent control over their intensity through the subcycle delay of the two-color fields. The odd harmonics are insensitive to the degree of orientation, but modulate with the degree of axis alignment, in agreement with calculated photorecombination dipole moments. We further compare the shape of the even and odd harmonic spectra with our calculations and determine the degree of orientation.

Making the best of mixed-field orientation of polar molecules: a recipe for achieving adiabatic dynamics in an electrostatic field combined with laser pulses

We have experimentally and theoretically investigated the mixed-field orientation of rotational-state-selected OCS molecules and achieved strong degrees of alignment and orientation. The applied moderately intense nanosecond laser pulses are long enough to adiabatically align molecules. However, in combination with a weak dc electric field, the same laser pulses result in nonadiabatic dynamics of the mixed-field orientation. These observations are fully explained by calculations employing both adiabatic and nonadiabatic (time-dependent) models.

Time-resolved photoelectron spectroscopy: from wavepackets to observables

Time-resolved photoelectron spectroscopy (TRPES) is a powerful tool for the study of intramolecular dynamics, particularly excited state non-adiabatic dynamics in polyatomic molecules. Depending on the problem at hand, different levels of TRPES measurements can be performed: time-resolved photoelectron yield; time- and energy-resolved photoelectron yield; time-, energy-, and angle-resolved photoelectron yield. In this pedagogical overview, a conceptual framework for time-resolved photoionization measurements is presented, together with discussion of relevant theory for the different aspects of TRPES. Simple models are used to illustrate the theory, and key concepts are further amplified by experimental examples. These examples are chosen to show the application of TRPES to the investigation of a range of problems in the excited state dynamics of molecules: from the simplest vibrational wavepacket on a single potential energy surface; to disentangling intrinsically coupled electronic and nuclear motions; to identifying the electronic character of the intermediate states involved in non-adiabatic dynamics by angle-resolved measurements in the molecular frame, the most complete measurement.

Intensified Reaction and Separation Systems

Process intensification follows four main goals: to maximize the effectiveness of intra- and intermolecular events, to give each molecule the same processing experience, to optimize the driving forces/maximize specific interfacial areas, and to maximize the synergistic effects of partial processes. This paper shows how these goals can be reached in reaction and separation systems at all relevant time and length scales and is focused on the structuring of reactors and separation units, on the use of different energy forms to improve the reaction and separation, on combining and superimposing of different phenomena in one integrated unit or reactor, and on the application of oscillations for intensification of reaction and separation processes.