E. Castellucci

Vibrational spectra and molecular conformation of cyclenes—I Vibrational assignment and valence force field of cyclohexene and cyclohexene-d10.

Abstract The infra-red and Raman spectra of cyclo hexene and cyclo hexene- d 10 have been studied between 4000 and 200 cm −1 . A vibrational assignment is given which is consistent with both the i.r. rotational band shapes and Raman depolarization data. The assignment is supported by a theoretical prediction of the fundamental frequencies calculated with a zero order valence force field. This force field was transferred from previous calculations on hydrocarbons and cyclo hexadiene 1–4, and it gave a correct interpretation of the experimental results. The force constants were then refined by the method of steepest descent. The resulting new force field can be used to predict the vibrational spectra of other cyclenes.

Infrared Spectra of Crystalline and Matrix Isolated Pyridine and Pyridine‐D5

Infrared spectra of pyridine‐H5 and pyridine‐D5 in the solid state were measured between 4000 and 200 cm− 1. Frequencies and polarization of fundamental absorptions were established for oriented thin films of freshly crystallized samples. Behavior of the bands in polarized light aided in clarifying several assignments. The multiplicity of several of the bands was accounted for by close‐lying overtones and combinations. Some of the components of ν26 are due to the existence of appreciable amounts of 13C isotope species clearly observable in a nitrogen matrix at 5°K. For pyridine‐D5 a phase transition was clearly observable after several hours of annealing of thin films at about − 60°C, but similar transformation could not be induced in normal pyridine. The infrared crystal data are consistent with an orthorombic factor group established by x‐ray analysis with no molecule on any symmetry element of the crystal. Raman spectra of liquid and solid pyridines are also reported.

The gas phase anisole dimer: a combined high-resolution spectroscopy and computational study of a stacked molecular system.

The gas phase structures of anisole dimer in the ground and first singlet electronic excited states have been characterized by a combined experimental and computational study. The dimer, formed in a molecular beam, has been studied by resonance-enhanced multiphoton ionization and high-resolution laser-induced fluorescence techniques. The assignment of the rotational fine structure of the S(1) <-- S(0) electronic transition origin has provided important structural information on the parallel orientation of aromatic rings of anisole moieties. By comparison with the DFT/TD-DFT computational results, it has been possible to infer the detailed equilibrium structure of the complex. The analysis of the equilibrium structure and interaction energy confirms that the anisole dimer is stabilized by dispersive interaction in the gas phase. This is, to the best of our knowledge, the first detailed work (reporting both theoretical and high-resolution experimental data) on an isolated cluster in the pi-stacking configuration.

Raman Spectrum of a Single Crystal of Benzene

The Raman spectrum of a single crystal of benzene at 140°K has been obtained using an argon ion laser source. The single crystals were oriented with the aid of a polarizing microscope. This technique was found suitable for low temperature work. Despite some cracking of the sample, the polarization was defined well enough to make the assignment of most librational lattice modes certain. The internal vibrations were also investigated, and for ν6, ν9, and ν10 the observed peaks have been assigned to their proper factor group species. The agreement between observed frequencies and those calculated in this laboratory is extremely good for the lattice vibrations, and acceptable for the internal modes.

Role of internal conversion on the excited state properties of trans-styrylpyridines

Abstract A theoretical and photophysical study of the three isomeric trans- n -styrylpyridines ( n = 2,3,4) has been carried out to evaluate the role of internal conversion (IC) on their deactivation pathways from the singlet manifold. Calculations by the QCFF/PI and CNDO/S methods and application of current theories of radiationless transitions allowed the rate constants for IC to be evaluated. The fluorescence lifetimes measured in the picosecond region and the fluorescence and trans → cis photoisomerization quantum yields from previous works allowed the rate constants for the non-radiative and non-reactive deactivation processes to be calculated. The experimental results were in a reasonable agreement with the theoretical predictions on the role of IC (markedly more important for the 2 and 4 derivatives) and confirmed that intersystem crossing is a low efficiency process for these azastilbenes. On the basis of the temperature and the solvent viscosity effects on the electronic spectra, an interpretation of the excitation energy effect on the quantum yields of the 3 isomer was attempted.

IR and Raman spectra of A 2,2′-bipyridine single crystal: internal modes☆

The polarized light IR and Raman spectra of 2,2′-bipyridine single crystals were obtained. The oriented gas model was applied and the proportionality factors for the intensity of the IR and Raman bands calculated and compared with experiment. The difficulties encountered while applying the oriented gas model to molecules with C2h symmetry and to monoclinic structures were discussed. An assignment of the internal modes based on the polarized light spectra has been given. The far infrared spectrum of the molecule was also measured and the ring—ring torsional model of Au species was identified at 73 cm−1.

Spectroscopic analysis of works of art using a single LIBS and pulsed Raman setup

A nanosecond pulsed laser setup has been optimized to perform laser-induced breakdown spectroscopy (LIBS) and pulsed Raman spectroscopy measurements in the field of cultural heritage. Three different samples of artistic/architectural interest with different typologies have been analyzed. The results from the two techniques allowed the identification of the materials used in their manufacture or contaminating them, probably coming from atmospheric pollution and biological activity. No sampling and sample preparation was required before the measurements, and no visual or structural damage was observed. Depth profiling using LIBS was performed in one of the samples, providing elemental information along the different layers composing the object and covering its surface. The quality of the results and the rather short time needed for the measurements and for switching between techniques confirmed the instrument’s capabilities and specificity for dealing with objects of artistic or historical interest.

Vibrational spectrum of 4-fluoraniline

The Raman spectrum of 4-fluoraniline (4FA) has been recorded, the quadratic force field has been calculated at RHF/631 1 G p level of theory and then scaled to reproduce the experimental frequencies, by using Pulay’s scaled quantum mechanical force field (SQMFF) methodology. Likewise, DFT force field has been calculated at the B3LYP/6-31 1 G p level. On the basis of all these results, a general assignment of the vibrational spectra of 4FA has been proposed and compared with that of aniline in order to determine the substitution effect of the fluorine atom. q 2001 Elsevier Science B.V. All rights reserved.

High-resolution absorption, excitation, and microwave-UV double resonance spectroscopy on a molecular beam: S1 aniline

Abstract A high-resolution, molecular beam UV spectrometer was constructed that uses both traditional laser induced fluorescence and optothermal detection of the energy content of the molecular beam. Microwave-UV double resonance capabilities were implemented to assist in the assignment of the UV spectra of medium-sized molecules with the ultimate goal to unravel their S1/T1 dynamics. It is shown that high quality optothermal spectra can be obtained in the 300 nm region, by recording the high-resolution, optothermally detected, S1 ← S0 0-0 absorption spectrum of aniline with a signal-to-noise ratio comparable to that of the LIF spectrum of the same band. The latter is used to obtain accurate rotational constants for the vibrationless S1 state of this molecule. Double resonance is demonstrated by confirming several rotational assignments in this way.

Normal mode analysis of 2,2′-bipyridine—II. Crystal vibrations

Abstract A normal mode analysis of the crystal spectrum of 2,2′-bipyridine was carried out using a previously determined intramolecular force field and an intermolecular potential described in terms of interactions among non-bonded atoms. New i.r. and Raman data in the region of lattice vibrations are presented, which can be satisfactorily accounted for by frequency calculations in the rigid-body approximation. Frequency splittings and shifts of internal modes, mixing with external vibrations and relative intensity of out-of-plane modes are analyzed through calculations at k = 0 which include all vibrational degrees of freedom.