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The ultraviolet photochemistry of vinylacetylene (C4H4) was studied under temperature and pressure conditions similar to Titan’s atmosphere by exciting the molecule in a constrained expansion that opens into the ion source region of a time-of-flight mass spectrometer. The primary dissociation products detected by vacuum-ultraviolet ionization were found to be C4H3 and C4H2, in a ratio of 3–10 : 1. Subsequent reaction of the C4H3 radicals with the parent C4H4 produced two major secondary products: C8H6 and C6H4. The former was spectroscopically identified as phenylacetylene, confirming that photochemical reactions of C4H4 can produce aromatic molecules. The primary dissociation reaction was also studied computationally. The results were consistent with the experimental findings for C4H2 and C4H3. However, the major product is C2H2, which is undetected by 118 nm photoionization in the present experiment but should account for roughly two-thirds of the products. Simulations were also performed to confirm that the present experiment accurately represents the 220 nm photochemistry of vinylacetylene at the temperature and pressure of Titan’s atmosphere, with a product yield of C2H2 : C4H2 : C4H3 of 66 : 7 : 27. Accounting for the wavelength dependent solar flux on Titan, the estimated absorption cross section of vinylacetylene in the ultraviolet, and the slightly wavelength dependent product distribution, the overall product yield predicted by the simulations for ultraviolet photolysis of vinylacetylene on Titan is C2H2 : C4H2 : C4H3 = 65 : 8 : 27. Finally, a simulation was performed under conditions of a shock tube experiment to examine the differences between thermal and photochemical dissociation. The product yield of this simulation was C2H2 : C4H2 : C4H3 = 61 : 1 : 38.

The potential energy surface (PES) of C4H4 was explored using quantum chemical methods (DFT, MP2, MP4, GVB-MP2, CCSD(T), G2M, CBSQ/APNO) and 43 different structures located at global and local minima were identified. The majority of these structures correspond to carbenes, a minority to closed shell systems and biradicals (carbyne structures were not investigated). Whereas the chemistry of the closed shell systems such as vinylacetylene (1), butatriene (2), methylenecyclopropene (3), cyclobutadiene (5) or tetrahedrane (15) is well known, the carbenes represent unusual structural entities. 2-Methyl-cycloprop-2-en-1-ylidene (4) (ΔΔH(298) = 36.2 kcal mol−1 relative to 1) in its σ2π0 electron configuration at the carbene C of the 1A ground state is of comparable stability to cyclobutadiene (5) (ΔΔH(298) = 33.4 kcal mol−1; exp. value: 32.1 kcal mol−1) as a result of aromatic 2π-delocalization; carbene 3-vinylidenecyclopropene (13) (ΔΔH(298) = 53.9 kcal mol−1) does not possess C2v symmetry but has the vinylidene group bent toward the three-membered ring (Cs-symmetry) thus representing a frozen path point of the chelotropic addition of :C&z.dbd;C: to ethene. Allenyl carbene (14) has a triplet ground state and two low lying excited singlet states of closed shell (2.5 kcal mol−1 higher) and open shell character (14.1 kcal mol−1). Carbene 14 is a crossing point on the C4H4 PES connecting closed-shell systems with each other. Because of the stability of 1, its rearrangement reactions are all connected with high activation enthalpies requiring 66 up to 92 kcal mol−1 so that they energetically overlap with the activation enthalpies typical of decomposition reactions (from 90 kcal mol−1 upward). The possible rearrangement reactions of 1 are investigated with a view to their relevance for the chemical behavior of the molecule under the conditions of Titan’s atmosphere.

We present the synthesis of substituted ketones, conjugated analogs of Michler’s ketone. These molecules exhibit broadband TPA properties between 700 and 1100 nm due to a charge transfer from the terminal amino groups to the central ketone function and with maximum cross sections from 200 to 325 × 10−50 cm4 s photon−1. Moreover, they present an interesting reducing character for radical creation. Both properties allow us to consider these molecules as promising photoinitiators of polymerization in the near infrared.

Both experimental and theoretical spectroscopic studies on small gas phase polycyclic aromatic hydrocarbons in the far-infrared spectral region are reported. The experimental set-up based on thermal emission and Fourier transform far infrared analysis led to the detection of relatively broad vibrational bands, unresolved in rotation, representative of each molecule. Detailed theoretical investigations were performed, including both ab initiocalculations and spectral simulations. For the majority of the samples, this study provides the first detection of the vibrational modes associated with the skeleton motions.

Fluorescence and phosphorescence spectra and decay times are recorded upon a narrow-band laser excitation for naphthalene N and quinoline Q embedded in xerogels prepared from MTEOSTEOS mixtures, in the 10–300 K temperature range. A site selectivity of the excitation is observed at T< 120 K and T< 150 K, for N and Q, respectively. In the case of quinoline, different families of sites are characterized. The results are discussed in terms of comparison with the N and Q emission behaviour in other environments, especially in rare-gas matrices.

We present measurements of low-energy 1–20 eV electron stimulated desorption ESD of H−from thin films of 5-halouracils 5-XU, X  F, Cl, Br and I condensed on polycrystalline Pt. The onset for H−desorption is ∼5.0 eV. For all 5-XU a single dissociative electron attachment DEA H−peak is observed, which is attributed to at least two dissociation channels at approximately 7.1 and 8.6 eV, resulting from N–H and C–H bond cleavage, respectively. Their relative contribution is parent-molecule dependent. Also, for a given molecule, these dissociation channels are affected differently by the metal, and the DEA maximum shifts by ∼0.5 eV as the film thickness increases. Above 10 eV, dipolar dissociation DD is the dominant H−formation mechanism. The yields of H−vary in the following relative order T  thymine, U  uracil: T > U > 5-FU > 5-ClU > 5-BrU > 5-IU. A model is developed to explain the film thickness dependence of the desorbed anion signal: above a coverage of ∼1 monolayer ML, the film thickness dependence of the H−ESD yield is interpreted in terms of incident electron and desorbing ion transmission within the films. The main difference in the thickness dependence of H−produced viaDEA and DD is attributed to the fact that electron transfer to the metal from the transient molecular anion leads to dramatic decrease in the H−ESD signal below ∼1 ML, whereas it does not affect significantly DD, since its intermediate state is neutral.

Photophysical, photochemical and electrochemical studies of a new series of heterobinuclear complexes of ruthenium and iron, RuIIbpy2LnFeIIbpy24bpy  2,2′-bipyridine, n  2 RuIIL2FeII4, n  4 RuIIL4FeII4, n  6 RuIIL6FeII4, issued from the linkage of the Rubpy32and Febpy32subunits by covalently bridging bis-bipyridine Ln ligands have been investigated. The cyclic voltammetry of the three complexes exhibits two successive metal-centered electron reversible oxidation processes, clearly separated, in the positive region. In the negative area, three successive reversible two electron waves are observed the second and the third being strongly distorted by adsorption phenomena corresponding to the ligand-based reduction processes. In addition, the two oxidized forms of these complexes RuIILnFeIII5and RuIIILnFeIII6obtained by two successive exhaustive electrolyses exhibit high stability, which is crucial for an efficient photocatalytic operating system. Luminescence of the complexes RuIILnFeII4has been observed indicating that the covalently linkage between the Rubpy32and Febpy32units leads to an only partial quenching of the RuII excited state by energy transfer to FeII. The nature of the energy transfer process involved in those heterobinuclear complexes is studied and an intermolecular electron exchange mechanism is proposed as a preferably deactivation route. On the other hand, the photoxidation of the RuIIsubunit into the RuIIIone could be easily obtained in the presence of a diazonium salt, playing the role of sacrificial oxidant. Finally photocatalytic oxidation of the complexes has been performed by continuous photolysis experiments. For each heteronuclear complexes, the multi-step oxidation process FeII → FeIIIand RuII → RuIII has been observed. The comparison with an isoconcentrated mixture of the corresponding homonuclear parent complexes has been made.