Real-time dynamics of vibronic wavepackets within Rydberg and ion-pair states of molecular iodine.

Real-time dynamics of vibrationally and electronically excited I molecules has been investigated experimentally using the pump-probe technique. A 2-photon excitation was performed either at 269 nm or 266 nm. An electronic and vibrational wavepacket was built as coherent superposition of a few (269 nm excitation) or many (266 nm excitation) Rydberg states of the and series partly coupled with ion-pair states.

Excited state dynamics of normal dithienylethene molecules either isolated or deposited on an argon cluster.

Real-time dynamics of the electronically excited open-ring isomer of 1,2-bis(2-methylbenzo[]thiophen-3-yl)perfluorocyclopentene (BTF6) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (PTF6) molecules was investigated using a set-up that associates a molecular beam, femtosecond lasers and velocity map imaging. The molecules were either free in the gas phase or bound to an argon cluster. DFT and TDDFT calculations were performed on BTF6.

Reaction dynamics within a cluster environment.

This perspective article reviews experimental and theoretical works where rare gas clusters and helium nanodroplets are used as a nanoreactor to investigate chemical dynamics in a solvent environment. A historical perspective is presented first followed by specific considerations on the mobility of reactants within these reaction media. The dynamical response of pure clusters and nanodroplets to photoexcitation is shortly reviewed before examining the role of the cluster (or nanodroplet) degrees of freedom in the photodynamics of the guest atoms and molecules.

Time-Resolved Observation of the Solvation Dynamics of a Rydberg Excited Molecule Deposited on an Argon Cluster. II. DABCO at Long Time Delays.

The real-time dynamics of DABCO-argon clusters is investigated in a femtosecond pump-probe experiment where the pump excites DABCO to the S state within the argon cluster. The probe operates by photoionization and documents the energy and angular distributions of the resulting photoelectrons. The present work complements a previous work from our group [Awali , 2014, 16, 516-526] where this dynamics was probed at short time, up to 4 ps after the pump pulse.

Vacuum-Ultraviolet Absorption Spectrum of 3-Methoxyacrylonitrile.

The high-resolution absorption spectrum of 3-methoxyacrylonitrile (3MAN) was measured between 5.27 and 12.59 eV using a synchrotron-based Fourier-transform spectrometer.

High-resolution vacuum ultraviolet absorption spectra of 2,3- and 2,5-dihydrofuran.

Using a synchrotron-based Fourier-transform spectrometer, the high-resolution absorption spectra of the C-symmetric 2,3-dihydrofuran (23DHF) and C-symmetric 2,5-dihydrofuran (25DHF) have been measured from 5.5 eV to 9.4 eV with an absolute absorption cross section scale.

Excited State Dynamics of Isolated 6- and 8-Hydroxyquinoline Molecules.

The photoinduced dynamics of isolated n-hydroxyquinoline (nHQ) molecules (n=6,8) was investigated in femtosecond pump-probe experiments. A qualitative difference was found between 8HQ and 6HQ. After an initial rapid decay corresponding to the departure of the initial wavepacket out of the Franck-Condon region of the excitation, the 8HQ probe signal decays to zero in 0.

Energetics and ionization dynamics of two diarylketone molecules: benzophenone and fluorenone.

Single photon ionization and subsequent unimolecular ion decomposition were studied on jet-cooled benzophenone and fluorenone separately, using VUV synchrotron radiation in a photoion/photoelectron coincidence setup. Slow PhotoElectron Spectra (SPES) were recorded in coincidence with either the parent or the fragment ions for hν < 12.5 eV.

A HElium NanoDroplet Isolation (HENDI) investigation of the weak hydrogen bonding in the propyne dimer (CHCCH).

A HElium Nanodroplet Isolation (HENDI) experiment was performed to explore the absorption spectra of the propyne monomer (CH3CCH), dimer and (CH3CCH)≥3 multimers in the vicinity of the CH stretch region ν1 of the monomer. Ab initio calculations were performed at the MP2 level to document the potential energy surface of the dimer. This provided the necessary parameters to simulate the absorption spectrum of the dimer and thus facilitate the interpretation of the experiment.

Large amplitude motion within acetylene-rare gas complexes hosted in helium droplets.

Near-infrared spectroscopy of the C2H2-Ar, Kr complexes was performed in the spectral region overlapping the ν3/ν2 + ν4 + ν5 Fermi-type resonance of C2H2. The experiment was conducted along the HElium NanoDroplet Isolation (HENDI) technique in order to study the coupling dynamics between a floppy molecular system (C2H2-Ar and C2H2-Kr) and a mesoscopic quantum liquid (the droplet). Calculations were performed using a spectral element based close-coupling program and state-of-the-art 2-dimensional potential energy surfaces to determine the bound states of the C2H2-Ar and C2H2-Kr complexes and simulate the observed spectra.

Large amplitude motions within molecules trapped in solid parahydrogen.

Molecules of the β-diketone and β-dialdehyde families were trapped in solid parahydrogen (pH2) to investigate the vibrational behavior of systems containing an intramolecular hydrogen bond (IHB). In the simplest β-diketone, acetylacetone (AcAc), H transfer related to the IHB is coupled with methyl torsions. In pH2, the study of nuclear spin conversion (NSC) in methyl groups allows the characterisation of the influence of these large amplitude motions on the vibrational modes.

Self-trapping relaxation decay investigated by time-resolved photoelectron spectroscopy.

The present work combines time-resolved photoelectron spectroscopy on isolated species with high-level data processing to address an issue which usually pertains to materials science: the electronic relaxation dynamics towards the formation of a self-trapped exciton (STE). Such excitons are common excited states in ionic crystals, silica and rare gas matrices. They are associated with a strong local deformation of the matrix.

Dynamics of acetylene dimers hosted in helium droplets.

The CH antisymmetric stretch of the CH moieties in acetylene dimers was explored over the range 3270-3290 cm using the helium nanodroplet isolation (HENDI) technique. This work is part of a general investigation which addresses the dynamical consequences of coupling the deformation motions of weakly bound complexes with a finite size quantum liquid (the helium droplet). The acetylene dimer is attractive from this point of view because one of its deformation coordinates promotes a tunneling isomerization process.

Multipronged mapping to the dynamics of a barium atom deposited on argon clusters.

The dynamics of an electronically excited barium atom deposited at the surface of an Ar cluster was explored in a multipronged approach which associates information from frequency-resolved nanosecond experiments and information from femtosecond time-resolved experiments. In both types of experiments, the dynamics is monitored by photoelectron and photoion spectroscopy.

Direct observation of slow intersystem crossing in an aromatic ketone, fluorenone.

Direct measurements of Single vibronic Level InterSystem Crossing (SLISC) have been performed on the fluorenone molecule in the gas phase, by time resolved photoelectron and photoion spectroscopy. Vibronic transitions above the S1 nπ* origin were excited in the 432-420 nm region and the decay of S1 and growth of T1(3)ππ* could be observed within a 10 ns time domain. The ionization potential is measured as 8.

Large amplitude motion of the acetylene molecule within acetylene-neon complexes hosted in helium droplets.

Superfluid helium droplets provide an ideal environment for spectroscopic studies with rotational resolution. Nevertheless, the molecular rotation is hindered because the embedded molecules are surrounded by a non-superfluid component. The present work explores the dynamical role of this component in the hindered rotation of C2H2 within the C2H2-Ne complex.

Ultrafast Excited-State Dynamics of a Cyano-Substituted "Proton Sponge".

The dynamics of a substituted proton sponge-the 1,8-bis(dimethylamino)-4-cyanonaphthalene (DMAN-CN) molecule-was investigated after excitation in the S1 state. Experimental and theoretical information are reported. The former includes absorption, fluorescence, and time-resolved transient absorption spectra, which were recorded in solution.

Absorption Spectroscopy, a Tool for Probing Local Structures and the Onset of Large-Amplitude Motions in Small KAr(n) Clusters at Increasing Temperatures.

Photoabsorption spectra of KArn (n = 1-10) are simulated at temperatures ranging between 5 and 25 K. The calculations associate a Monte Carlo (MC) method to sample cluster geometries at temperature T, with a one-electron ab initio model to calculate the ground-state and excited-state energies of the cluster. The latter model replaces the K(+) core electrons and all the electrons of the Ar atoms by appropriate pseudopotentials, complemented by core polarization potentials.

Photoionization of Benzophenone in the Gas Phase: Theory and Experiment.

We report on the single photoionization of jet-cooled benzophenone using a tunable source of VUV synchrotron radiation coupled with a photoion/photoelectron coincidence acquisition device. The assignment and the interpretation of the spectra are based on a characterization by ab initio and density functional theory calculations of the geometry and of the electronic states of the cation. The absence of structures in the slow photoelectron spectrum is explained by a congestion of the spectrum due to the dense vibrational progressions of the very low frequency torsional mode in the cation either in pure form or in combination bands.

Spectroscopy and Dynamics of K Atoms on Argon Clusters.

We present a combined experimental and simulation study of the 4s → 4p photoexcitation of the K atom trapped at the surface of ArN clusters made of a few hundred Ar atoms. Our experimental method based on photoelectron spectroscopy allows us to firmly establish that one single K atom is trapped at the surface of the cluster. The absorption spectrum is characterized by the splitting of the atomic absorption line into two broad bands, a Π band associated with p orbitals parallel to the cluster surface and a Σ band associated with the perpendicular orientation.

Reactive and Inelastic Channels in the Ca*···FCH3 Transition State: A Simple Branching Mechanism.

To study the excited state dynamics between a calcium atom and the CH3F molecule, a Ca···CH3F 1:1 complex has been prepared by a supersonic expansion with laser ablation of calcium metal in the gas phase. Tunable laser excitation of these complexes in molecular states correlating to Ca (1)P1(4s4p) + CH3F allows observing two competitive channels: the direct dissociation and the reactive channel into CaF* + CH3. The translational recoil, as well as the alignment of the fragments Ca* and CaF* have been analyzed by velocity map imaging and time-of-flight mass spectrometry.

Coupled electronic and structural relaxation pathways in the postexcitation dynamics of Rydberg states of BaArN clusters.

We investigate, theoretically, the joint relaxation of orbital and structure in postexcitation dynamics of Rydberg states of cluster BaArN (N=250). Mixed quantum-classical dynamics is used to account for the nonadiabatic transitions among more than 160 electronic states, represented via a diatomics-in-molecules Hamiltonian. The simulation illustrates the complex multistep relaxation processes and provides detailed insight in the mechanisms contributing to the final-time experimental photoelectron spectrum.

Competitive direct vs. indirect photochromism dynamics of constrained inverse dithienylethene molecules.

State-of-the-art experimental and theoretical tools were used to investigate the gas-phase relaxation dynamics of various photoexcited photochromic dithienylethene molecules in situations where several relaxation channels are simultaneously at play. Unconstrained and constrained dynamics were addressed by considering unbridged and bridged molecules with a polyether bridge of various sizes (from 2 to 4 units). Time-resolved ultrafast ionization spectroscopy techniques were used to probe the dynamics.

Gas phase dynamics of triplet formation in benzophenone.

Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0.