Andreas Beil

COMBINED HIGH RESOLUTION INFRARED AND MICROWAVE STUDY OF BROMOCHLOROFLUOROMETHANE

We report a detailed spectroscopic investigation of the chiral molecule bromochlorofluoromethane (CHBrClF) with rotational resolution using a pulsed nozzle beam Fourier transform microwave (FTMW) and a waveguide FTMW spectrometer as well as a supersonic jet interferometric Fourier transform infrared (FTIR) and infrared diode laser spectrometer. The rotational spectrum of CHBrClF has been measured between 8 and 18 GHz. The quadrupole hyperfine components have been fully resolved for the assigned rotational transitions with J⩽18. Three ground state rotational constants, five centrifugal distortion constants, and all five independent elements of the bromine and chlorine quadrupole coupling tensors have been determined for each of the four isotopomers CH79Br35CIF, CH81Br35CIF, CH79Br37CIF, and CH81Br37CIF from about 500 measured transition frequencies of the hyperfine components. The quadrupole coupling tensor has been transformed to its principal axes. The determinable sign combinations of the off-diagonal e...

Vibrational spectra and intramolecular vibrational redistribution in highly excited deuterobromochlorofluoromethane CDBrClF: Experiment and theory

The rovibrational spectra of deuterobromochlorofluoromethane (CDBrClF) were measured at intermediate (0.1 cm−1) and high resolution (0.0024 cm−1 full bandwidth, half-maximum) by interferometric Fourier transform infrared spectroscopy in the range from the far infrared at 200 cm−1 to the near infrared (12 000 cm−1) covering all the fundamentals and CD stretching overtones up to polyad N=5. The spectra are completely analyzed in terms of their vibrational assignments to fundamentals, combinations and overtones. At high excitation the analysis reveals the dominant anharmonic coupling between four high frequency vibrational modes; the CD stretching (ν1), two CD bending (ν2,ν3), and the CF stretching mode (ν4). The analysis is carried out using effective model Hamiltonians including three and four vibrational degrees of freedom. We also present vibrational variational calculations on a grid in a four-dimensional normal coordinate subspace. The potential energy and the dipole moment function are calculated ab initio on this grid using self-consistent field second order Moller–Plesset perturbation theory (MP2). Experimental and theoretical results for band positions and integrated intensities as well as effective spectroscopic parameters are found to be in good agreement. The important anharmonic coupling between the CD chromophore and the CF stretching vibration can be described by an effective cubic Fermi resonance coupling constant ksff′≈(50±10) cm−1, which leads to intramolecular vibrational redistribution between the CD and CF chromophores on the femtosecond time scale. Time dependent intramolecular vibrational redistribution processes in CDBrClF are derived in various representations, including time dependent probability densities (“wave packets”) in coordinate space and finally time dependent entropy.The rovibrational spectra of deuterobromochlorofluoromethane (CDBrClF) were measured at intermediate (0.1 cm−1) and high resolution (0.0024 cm−1 full bandwidth, half-maximum) by interferometric Fourier transform infrared spectroscopy in the range from the far infrared at 200 cm−1 to the near infrared (12 000 cm−1) covering all the fundamentals and CD stretching overtones up to polyad N=5. The spectra are completely analyzed in terms of their vibrational assignments to fundamentals, combinations and overtones. At high excitation the analysis reveals the dominant anharmonic coupling between four high frequency vibrational modes; the CD stretching (ν1), two CD bending (ν2,ν3), and the CF stretching mode (ν4). The analysis is carried out using effective model Hamiltonians including three and four vibrational degrees of freedom. We also present vibrational variational calculations on a grid in a four-dimensional normal coordinate subspace. The potential energy and the dipole moment function are calculated ab i...

Rotational analysis of the ν1 band of trichlorofluoromethane from high resolution Fourier transform and diode laser spectra of supersonic jets and isotopically enriched samples

The spectrum of CCl3F (trichlorofluoromethane, CFC 11) has been measured in the region of the ν1 fundamental (1050–1120 cm−1) by high resolution interferometric Fourier‐transform spectroscopy [0.004 cm−1 bandwidth full width at half maximum, apodized] and by diode laser spectroscopy (bandwidth 0.0008–0.0020 cm−1 FWHM) at room temperature, in cold cells and in supersonic jet expansions. Fourier‐transform infrared and diode laser spectra of isotopically pure C35Cl3F have been recorded at room temperature in static cells. The C35Cl3F spectra allowed an analysis of the rotational structure to be started successfully for the first time. The rotational analysis of the isotopic species C35Cl237ClF and C35Cl37Cl2F, which are asymmetric rotors, was initiated from diode laser spectra of natural CCl3F with a rotational temperature of about 20 K (5% seeded in He) resulting from expansion in a supersonic pulsed slit jet. The rotational analysis yielded effective Hamiltonian constants including accurate band centers fo...

Sub-Doppler supersonic jet spectra of the coupled 6a10 and 6b10 vibronic bands of the S1(1B2u) ← S0(1A1g) transition in monodeuterobenzene and their rovibrational analysis

We report the rotationally resolved spectra of C6H5D obtained in a supersonic seeded jet by Doppler free UV laser spectroscopy with an effective resolution of about 0·0045 cm-1. The coupled 6a1 0 and 6b1 0 vibronic transitions are analysed in terms of their spectroscopic constants ( = 38 634·2429 cm-1 for 6a1 0 and = 38 637·1792 cm-1 for 6b1 0) and the Coriolis coupling constant ξc 6 = 0·095 85 cm-1, obtained by constraining the C rotational constants to be equal for 6a1 and 6b1. Simulations of the spectra result in rotational temperatures of about 2K. The polarizations of the two transitions could be determined unambiguously as well as the approximate ratio of the transition moments.

Excited vibrational states of benzene: High resolution FTIR spectra and analysis of some out-of-plane vibrational fundamentals of C6H5D

Abstract We have measured the infrared spectra of the ν 4 , ν 10b and ν 11 fundamental bands of C 6 H 5 D in the range 540–830 cm −1 with an instrumental bandwidth of 0.0024 cm −1 (unapodized FWHM) using a Bomem DA 002 Interferometric Fourier Transform spectrometer. The rotational analysis for ν 4 yields ground state constants by combining ground state combination differences and published microwave data (M. Oldani and A. Bauder, Chem. Phys. Lett. 108 (1984) 7). Excited state constants for the ν 4 level were obtained up to quartic terms, using Watsons A-reduction Hamiltonian in the III r representation, resulting in a band center ν 4 0 =697.593 cm −1 . A partial analysis is presented for the ν 10b fundamental ( ν 10b 0 =778.027 cm −1 ), which appears to be locally perturbed by the ν 16a + ν 16b combination band. The very strong ν 11 band is strongly perturbed, most probably by ν 6a and ν 6b . The results are discussed in relation to comparison with accurate ab initio electronic structure calculations including non Born-Oppenheimer effects as well as potential applications with isotope tracer detection and infrared laser chemistry.

Intramolecular energy transfer and vibrational redistribution in chiral molecules: experiment and theory

The quantum vibrational dynamics of the CH-chromophore in a chiral environment are studied with the examples CHDTMu, CHDTF and CHFClBr. For the chiral methane isotopomer we use a recently established nine-dimensional potential hypersurface to extract the three-dimensional short-time quantum dynamics and the related CH-overtone spectra. We have carried out ab initio(MP2) calculations in the appropriate normal coordinate subspace for CHDTF, a chiral isotopomer of methylfluoride for which we have previously carried out extensive related calculations, and also experimental investigations on other isotopomers. For CHFClBr we report the first experimental and theoretical study of the CH-chromophore overtone spectra. The results are systematically analysed in terms of anharmonic coupling constants of the effective hamiltonian as well as the potential hypersurfaces in the appropriate three-dimensional subspaces. We show that the chiral, symmetry-breaking coupling constant ksab is of appreciable absolute magnitude for all three cases (ca. 25 cm–1 for CHFClBr). The resulting fast intramolecular vibrational redistribution in the highly excited CH-chromophore, on the femtosecond timescale, leads to appreciable population transfer between states of dynamical a′ and a″ symmetry for the electronically, ‘chemically’ chiral CHFClBr and for CHDTF, which is chiral only by isotope substitution. The symmetry-breaking intra-molecular redistribution processes in chiral molecules are briefly discussed in relation to dynamical chirality, time-dependent optical activity and fundamental symmetry violations of parity, and even of charge conjugation, parity and time-reversal symmetry and their combinations.

Bismesitoylphosphinic Acid (BAPO‐OH): A Ligand for Copper Complexes and Four‐Electron Photoreductant for the Preparation of Copper Nanomaterials

Bismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO-OH), is an efficient photoinitiator for free-radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO-OH as the ligand. The complex CuII (BAPO-O)2 (H2 O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO-OH, which serves as a four-electron photoreductant.