Experimental and theoretical study of resonant core-hole spectroscopies of gas-phase free-base phthalocyanine.

We studied N 1s-1 inner-shell processes of the free base Phthalocyanine molecule, H2Pc, in the gas-phase. This complex organic molecule contains three different nitrogen sites defined by their covalent bonds. We identify the contribution of each site in ionized, core-shell excited or relaxed electronic states by the use of different theoretical methods. In particular, we present resonant Auger spectra along with a tentative new theoretical approach based on multiconfiguration self-consistent field calculations to simulate them. These calculations may pave the road towards resonant Auger spectroscopy in complex molecules.

Action spectroscopy of spin forbidden states in the gas phase: A powerful probe for large non-luminescent molecules.

Triplet action spectra of two similar copper porphyrins, copper tetraphenylporphyrin (CuTPP) and copper octaethylporphyrin (CuOEP), have been studied in the gas phase at low temperatures in the absence of external perturbations by using a resonant pump and a 193 nm probe, ionizing the 3ππ* orbital localized on the porphyrin cycle. The molecules were prepared by laser desorption in a disk source, then cooled in a helium supersonic expansion, and finally excited in the Q band system (S1 ← S0). This type of experiment allows the spectroscopic characterization of large non-luminescent molecules in the absence of solvent perturbations. The two copper porphyrins exhibit a broad electronic origin Q00 absorption spectrum, partly caused by the short lifetime of the excited (S1) state. The two porphyrins differ strongly with a strong Q00 band for CuOEP and a weak one for CuTPP, in agreement with the Gouterman four-orbital model. The two molecules exhibit different solvent shifts: CuOEP is blue shifted in non-polar solvents owing to its alkyl substituents, while CuTPP is red shifted as for regular transitions to ππ* orbitals. The decay dynamics of the triplet state exhibit a collision-free lifetime of 70 ± 7 ns for CuTPP atop a microsecond decay. This non-exponential decay can be viewed as evidence of time evolution of two states combining the state with spin 1 borne by the porphyrin ring and that by the Cu atom 12. Therefore, this method allows solvent-free spectrodynamics of large molecules in a short microsecond time range.

A HElium NanoDroplet Isolation (HENDI) investigation of the weak hydrogen bonding in the propyne dimer (CH3CCH)2.

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. The central result was to observe three isomers of the dimer, hence reflecting the complexity of the weak CHπ H-bonding when several H-donors are at play.

Dynamics of acetylene dimers hosted in helium droplets.

The CH antisymmetric stretch of the C2H2 moieties in acetylene dimers was explored over the range 3270-3290 cm-1 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. A numerical simulation of the observed spectrum allows deriving a set of effective spectroscopic constants which help understanding the dynamical role played by the droplet on the rotation and deformation of the dimer.

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≈500 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.

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. A HENDI experiment was built and near-infrared spectroscopy of C2H2-Ne and C2H2 was performed in the spectral region overlapping the ν3/ν2 + ν4 + ν5 Fermi-type resonance of C2H2. The comparison between measured and simulated spectra helped to address the above issue.

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. This revealed that both the dissociation and reaction processes are quasi direct and are of comparable intensity. We provide a simple interpretation for this process: the electronically excited potential surface of the Ca*···FCH3 complex initiates a fast predissociation from a suspended well to two repulsive surfaces that lead either to Ca (1)P1(4s4p) (Ω = 1) + CH3F or to CaF((2)Δ) + CH3.

Fluorescence emission of Ca-atom from photodissociated Ca2 in Ar-doped helium droplets. I. Experimental.

The Ca(2) → Ca(4s4p(1)P) + Ca(4s(2)(1)S) photodissociation was investigated in a He droplet isolation experiment where the droplets are doped by Ar atoms. Fluorescence spectra associated with the Ca(4s4p(1)P → 4s(2)(1)S) emission were recorded as a function of the average number of Ar atoms per droplet. Three contributions were observed depending on whether the emitting Ca atoms are free, bound to helium atoms or bound to argon atoms. Moreover, the full Ca(4s4p(1)P → 4s(2)(1)S) fluorescence emission was recorded as a function of the wavelength of the photodissociation laser, hence providing the action spectrum of the Ca(2) → Ca(4s4p(1)P) + Ca(4s(2)(1)S) process. The latter spectrum suggests that in He droplets doped by argon, Ca atoms are attracted inside the droplet where they associate as Ca(2). Full analysis of the spectra indicate that the emission of Ca bound to a single Ar atom is redshifted by 94 cm(-1) with respect to the emission of free Ca.

Fluorescence emission of Ca-atom from photodissociated Ca2 in Ar doped helium droplets. II. Theoretical.

The stability of the ground or excited state calcium atom in an argon-doped helium droplet has been investigated using an extension of the helium density functional method to treat clusters. This work was motivated by the experimental study presented in a companion paper, hereafter called Paper I [A. Masson, M. Briant, J. M. Mestdagh, M. A. Gaveau, A. Hernando, and N. Halberstadt, J. Chem. Phys. 137, 184310 (2012)], which investigated Ca(2) photodissociation in an argon-doped helium droplet and the nature of the fluorescent species. It is found that one single argon atom is sufficient to bring the calcium atom inside the droplet, for droplets of over 200 helium atoms. The absorption and emission spectra of CaAr(M) (M = 0-7) clusters have been simulated using the recently developed density sampling method to describe the influence of the helium environment. Absorption spectra exhibit broad, double bands that are significantly blueshifted with respect to the calcium atomic line. The emission spectra are less broad and redshifted with respect to the calcium resonance line. The shifts are found to be additive only for M ≤ 2, because only the first two argon atoms are located in equivalent positions around the calcium p orbital. This finding gives a justification for the fit presented in the companion paper, which uses the observed shifts in the emission spectra as a function of argon pressure to deduce the shifts as a function of the number of argon atoms present in the cluster. An analysis of this fit is presented here, based on the calculated shifts. It is concluded that the emitting species following Ca(2) photodissociation in an argon-doped droplet in Paper I could be Ca∗Ar(M) in a partly evaporated droplet where less than 200 helium atoms remain.

Observation of a barium xenon exciplex within a large argon cluster.

Spectroscopic measurements provide fluorescence and excitation spectra of a single barium atom codeposited with xenon atoms on argon clusters of average size approximately 2000. The spectra are studied as a function of the number of xenon atoms per cluster. The excitation spectrum with approximately 10 xenon atoms per cluster is qualitatively similar to that observed when no xenon atom is present on the cluster. It consists of two bands located on each side of the 6s6p (1)P-6s(2) (1)S resonance line of the free barium. In contrast, the fluorescence spectrum differs qualitatively since a barium-xenon exciplex is observed, which has no counterpart in xenon free clusters. In particular an emission is observed, which is redshifted by 729 cm(-1) with respect to the Ba(6s6p (1)P-6s(2) (1)S) resonance line.

[Severe Moorens ulcer: efficacy of monthly cyclophosphamide intravenous pulse treatment]. / Ulcères de Mooren sévères: efficacité du traitement par cyclophosphamide en bolus intraveineux mensuels.

PURPOSE: Mooren's ulcer (MU) is a chronic peripheral corneal ulceration featuring conjunctival immunoglobulin deposits. It is considered as the result of a limbic immune process with hyperactivation of T and B lymphocytes. The etiology remains unknown. The response to topical steroid therapy and surgical procedures usually poor and the visual outcome can be devastating. METHODS: Clinical follow-up of 3 patients who had rebel MU to conventional therapy, and were treated with 1g monthly intravenous cyclophosphamide. RESULTS: First patient was a 24-years-old man who had MU in his left eye. The response to surgical procedure and intravenous steroid treatment was poor and corneal perforation occurred. The affected cornea healed after 9 months of Cy treatment. The second patient was a 50-years-old man who had MU in his left eye, which did not improved with lamellar keratoplasty and topical steroid therapy. Corneal healing was obtained after 20 months of Cy treatment. The third patient was a 70-years-old man who presented with a furrowed MU in his right eye which healed with conjunctival resection and 4 months of Cy perfusion. No adverse effects of Cy was noted as opposed to Cy given orally. CONCLUSION: We report the effectiveness of 1g monthly intravenous cyclophosphamide (Cy) treatment in rebel MU. We suggest that immunosuppressive therapy using IV monthly Cy may be proposed in severe rebel MU.

Excited state reactions of metals in clusters: pluridimensional harpoon and solvation effects.

Excited state reactions of metals produce electronically excited products efficiently, as revealed by studies performed both in the gas phase and in free Van der Waals complexes. The reaction mechanism is assigned to an excited state charge transfer from the metal to the molecular reactant (i.e. a harpoon mechanism). The present work uses the well established cluster isolated chemical reaction (CICR) technique and addresses these processes when the metal ... molecule Van der Waals pair is deposited at the surface of a large argon cluster. Such work is aimed at investigating the effect of the cluster substrate on the preparation and dynamics of the reaction. We have revisited the pluridimensional character of the harpoon reaction in these systems. More specifically, we studied the reaction of excited calcium with HBr near the calcium resonance line at 422.7 nm, forming CaBr in the A and B states. As in previous Van der Waals experiments, we could explore the dynamics of the reaction by recording action spectra. These spectra exhibit noticeable differences from those observed for unsupported Ca...HBr complexes. In particular the bending movement of the Ca...HBr complex which gives access to the transition state of the reaction is partly hindered by the presence of the argon cluster.

5-(Trifluoromethyl)-beta-l-2'-deoxyuridine, the L-enantiomer of trifluorothymidine: stereospecific synthesis and antiherpetic evaluations.

As a part of our ongoing work on beta-L-nucleoside analogues as potential antiviral drugs, we have synthesized 5-(trifluoromethyl)-beta-L-2'-deoxyuridine (L-TFT), the hitherto unknown L-enantiomer of trifluorothymidine (CF(3)dUrd, TFT). We have also studied the effect of L-TFT on human and herpes simplex virus (HSV) type 1 and 2 thymidine kinases, and human thymidine phosphorylase, as well as its anti-HSV-1 and anti-HSV-2 activities in cell cultures. L-TFT has been found: (i) to inhibit HSV-1 TK with activity comparable to TFT, with no effect on human TK, (ii) to be phosphorylated by the viral enzyme with similar efficiency to TFT, (iii) to be resistant, in contrast to TFT, to hydrolysis by human thymidine phosphorylase. Unfortunately, when evaluated in cell cultures, L-TFT did not show any anti-HSV-1 and anti-HSV-2 activities.