Surface vibrations of atoms physisorbed on a crystal surface: monolayer and bilayer xenon on (0001) graphite

Surface atom vibrations of monolayer and bilayer xenon physisorbed on (0001) graphite are studied with H atom scattering. The temperature dependence of the mean square displacement of surface atoms is obtain through measurements of the Debye-Waller factor. The monolayer data are consistent with LEED measurements and calculations using the Einstein model. The bilayer data lie between the monolayer and calculations for the (111) surface of solid xenon.     

UV spectra of benzene isotopomers and dimers in helium nanodroplets

We report spectra of various benzene isotopomers and their dimers in helium nanodroplets in the region of the first Herzberg-Teller allowed vibronic transition 6(0)(1) (1)B(2u)<--(1)A(1g) (the A(0) (0) transition) at approximately 260 nm. Excitation spectra have been recorded using both beam depletion detection and laser-induced fluorescence. Unlike for many larger aromatic molecules, the monomer spectra consist of a single "zero-phonon" line, blueshifted by approximately 30 cm(-1) from the gas phase position. Rotational band simulations show that the moments of inertia of C(6)H(6) in the nanodroplets are at least six-times larger than in the gas phase. The dimer spectra present the same vibronic fine structure (though modestly compressed) as previously observed in the gas phase. The fluorescence lifetime and quantum yield of the dimer are found to be equal to those of the monomer, implying substantial inhibition of excimer formation in the dimer in helium.     

Thermal detection laser spectroscopy of molecular beams

We describe the experimental methods used in carrying out high resolution infrared spectroscopy of molecular beams using bolometric thermal detection. The main applications of this technique are also described and include: studies on molecular internal vibrational relaxation, radiationless transition after “visible” excitation, photodissociation spectroscopy of van der Waals molecules, the study of coherent excitation of molecules in the infrared, multiphoton infrared spectroscopy, overtone spectroscopy and the study of large molecular clusters.     

Fluorinated aminoalkoxide and ketoiminate indium complexes as MOCVD precursors for In2O3 thin film deposition

The syntheses of two distinctive types of indium complex derived from trimethylindium (InMe(3)) are reported. The first kind has a generalized structural formula [InMe(2)(amak)](2), where (amak)H is an abbreviation for a series of chelating amino alcohol ligands HOC(CF(3))(2)CH(2)NHR, R = (CH(2))(2)OMe (1), Me (2), and Bu(t) (3), as well as HOC(CF(3))(2)CH(2)NMe(2) (4); while the second type of complex is illustrated by [InMe(2)(keim)] (5), for which (keim)H is a tridentate ketoimine ligand of structural formula O=C(CF(3))CH(2)C(CF(3))=NCH(2)CH(2)NMe(2). The solid-state structures of 2 and 5 were determined using single crystal X-ray diffraction studies. For the aminoalkoxide complexes 2-4, the existence of dimeric In(2)O(2) core structures in the solid state has been established with the amino fragment located trans to the alkoxide ligands, in a molecular arrangement which is in contrast to the distorted, trigonal bipyramidal geometry observed for the ketoiminate complex 5. Moreover, VT NMR studies of 2 revealed a rapid dimer-to-monomer equilibration and simultaneous rupture of the N-->In dative interaction, affording two interconvertible isomers related by having the N-Me substituents in either trans or cis dispositions. For complexes 2 and 5, deposition of In(2)O(3) thin films was successfully conducted at temperatures 400-500 degrees C, using O(2) as the carrier gas to induce indium oxide deposition and to suppress carbon impurity present in the thin film. Scanning electron micrographs (SEMs) revealed the surface morphologies. The atomic composition of these films was examined by both X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering (RBS) methods, while X-ray diffraction studies (XRD) confirmed the formation of a preferred orientation along the (222) planes.     

Supersonic beam spectroscopy of low J transitions of the ν3 band of SF6: Rabi oscillations and adiabatic rapid passage with a CW laser

The P(3) and P(4) manifolds of the ν₃ band of SF₆ have been observed in a supersonic beam with a bolometric detection. The influence of the laser beam divergence on the excitation efficiency has been studied. Rabi oscillations are observed when the wavefront is flat in the interaction region whereas only adiabatic rapid passage occurs when the molecules see a curved wavefront.     

The intramolecular dynamics of allene in the region around 6000 cm via eigenstate resolved IR spectroscopy

We have recorded and analyzed the molecular beam spectra of allene in the regions of the ν₁ + ν₅ and 2 ν₈ bands around 5947.5 and 6135.5 cm⁻¹, respectively. The ν₁ + ν₅ band only shows minor perturbations and we suspect the presence of a doorway state that causes parallel Coriolis coupling to the bath states. Perpendicular Coriolis interactions do not seem to play an important role since the size of the matrix elements does not increase systematically with J′. The spectrum in the region of the 2 ν₈ band is more complicated; a total of six sub-bands has been identified with K = 0–2. Based on the lack of any systematic dependence on J′ and an inverse dependence of the coupling on K, we expect that neither parallel nor perpendicular Coriolis coupling is present in this band. The effective lifetime for both bands is calculated to be about 200 ps, which is very similar to the lifetimes of an acetylenic C---H stretch overtone.     

Scattering experiments with hydrogen atoms. I. Differential collision cross sections for H + Ar,D + Ar and H + CH4

Differential collision cross section measurements for the scattering of hydrogen and deuterium atoms from argon and methane have been carried out with a crossed beams scattering apparatus which uses an oscillating supersonic beam as scattering target and a cryogenic bolometer as beam detector. Diffraction oscillations have been clearly resolved. The data are analyzed with a best fit computing procedure in terms of simple intermolecular energy functions. Well depth parameters for both Ar and CH₄ are 60% larger as compared with those predicted by the geometric mean combination rule while the experimental minimum of the well positions are 10% smaller as given by the arithmetic mean combining rule.     

Non-spherical potentials and molecular scattering at thermal energies. Nitrogen and the noble gases

High resolution differential collision cross section measurements for the systems N₂-Ar, N₂-Kr and N₂-N₂ are presented and compared with equal resolution Ar-Ar data. The quenching of the amplitude of the rainbow oscillation in the cross section is consistent with theoretical predictions.