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 elements of the coupling tensor have been evaluated. Rotational transitions involving high J were measured by FTIR spectroscopy between 15 and 40 cm−1 (450–1200 GHz) using a light pipe cell, providing an estimate of the permanent dipole moment |μ|=(1.5±0.3) D from intensities. In the midinfrared, we have fully analyzed the rovibrational line structure of supersonic jet spectra of the CF-stretching fundamental ν4, giving band centers for the isotopomers CH79Br35CIF [ν̃ 40=1077.178 43(4) cm−1], CH81Br35CIF [ν̃=1077.133 06(4) cm−1], CH79Br37CIF [ν̃ 40=1076.7914(4) cm−1], and CH81Br37CIF [ν̃ 40=1076.730 26(5) cm−1]. A combined analysis of about 20 microwave frequencies, more than 100 infrared ground state combination differences, and about 70 infrared transition frequencies for each of the35Cl isotopomers finally provide accurate ground and excited state rotational parameters as well as structural parameters, which may be compared to ab initio calculations. The results are discussed in relation to the molecular structure as well as coincidences of ν4 absorptions with CO2 laser lines in view of CO2–laser pumping and possible spectroscopic studies of this chiral molecule at ultrahigh resolution.

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-' for CHFClBr). The resulting fast intramolecular vibrational redistribution in the highly excited CHchromophore, 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 timereversal symmetry and their combinations.

Reactions of the parent phosphinidene-carbene adduct (Dipp)NHC = PH with chlorophosphanes are reported herein. The obtained (Dipp)NHC-substituted chlorodiphosphanes, (Dipp)NHC = P-PClR, and the formation of their cationic derivatives, [(Dipp)NHC-P = PR](+), were also explored. Depending on the steric demand of their substituents, these cations were found to be monomeric [(Dipp)NHC-PP-N(i)Pr2][GaCl4] or to dimerise to cyclotetraphosphanes [(Dipp)NHC-PP-R]2[GaCl4]2 (R = Ph, NMe2). For R = NMe2, this dication is the first isolated example of a tetrasubstituted all-σ(3) cyclotetraphosphane. Finally, the hetero-Diels-Alder reactivity of these cations was studied with 2,3-dimethylbuta-1,3-diene and cyclopentadiene, resulting in the isolation of a number of cationic 1,2-diphosphinanes.

The rovibrational spectra of bromochlorofluoromethane (CHBrClF) were measured at intermediate (0.1 cm-I ) and high resolution (0.001 cm-') between the far infrared (20cm-') and the visible range of the spectrum (14OOO cm -I ) by interferometric Fourier transform techniques and diode laser techniques in stationary samples and supersonic jets. All fundamentals and numerous combinations and overtone transitions could be assigned and their band positions and integrated strengths were determined. A quantitative interpretation of the complex multiple resonance structure of the CH chromophore spectra (about 50 assigned bands) is given in terms of an effective anharmonic CH-stretching-bending Hamiltonian and in terms of vibrational variational calculations on a 3-dimensional grid using ab initio (MP2 and B3LYP) and empirically adjusted potential hypersurfaces for the CH chromophore normal coordinate subspace. The systematic analysis of anharmonic resonances of the alkyl CH chromophore in symmetric top (C3J and asymmetric top (C,) molecules is herewith extended to chiral molecules. We provide a detailed analysis of the chiral C, symmetry breaking coupling in the effective Hamiltonian (coupling constant lkIabl =(20* 10) cm-') and in the potential (Csab and further terms) and their relationship. The implications for the femtosecond intramolecular dynamics for CHBrClF are discussed in terms of quantum dynamical results for time-dependent populations, survival probabilities, wavepackets and also timedependent symmetries and their violations (formal a' and a" species for vibrational C, and I quantum number for vibrational C,, symmetry). We have also developed an improved synthesis of CHBrClF, which is suitable for the preparation of large quantities (several mol) of the pure (racemic) compound, and have demonstrated enantiomer separation by gas chromatography.

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 Møller–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.

We present the conceptual background for intramolecular vibrational (rotational) redistribution (IVR) in polyatomic molecules and its analysis from high resolution spectra. We illustrate some of the basic concepts relating to the use of effective and real molecular hadtonians for IVR with examples drawn from our previous spectroscopic investigations of the chiral molecule CHFClBr. The importance of the initial state for the dynamics is shown, demonstrating that simple intuitive concepts of survival probabilities for some arbitrary chromophore ("zero order bright") state are insufficient for a quantitative understanding of IVR. An approximate (C,-like) symmetry prevents relaxation towards quasi-equilibrium in highly excited C,-asymmetrical CHFClBr. The coherent infrared multiphoton excitation of CHFClBr at the CH-stretching frequency leads to coherent vibrational states with a very wide energy distribution corresponding to short time oscillatory behaviour of the CHstretching motion with a period of 11 -12 fs. On longer time scales between 50 and 500 fs substantial vibrational motion is found in the CH-bending coordinates. For modest excitation energies both the initial vibrational angular momentum quantum number ([ = 0) and a' symmetry of the wavepacket are well conserved for 1 -2 ps. At higher excitations and longer times (2-4 ps) these approximate symmetries are lost. These results are briefly discussed in relation to a general classification of IVR mechanisms and in relation to reactive processes in CHFClBr.dations of IVR(R). Consider a molecular hamiltonian Rm in the space of s vibrational (-rotational) coordinates for internal motion in the center of mass system in IVR Bet Eunsenges. Phys. Chem. 101, 311 -328 (1997) No. 3 0 VCH Verlagsgeseilschafl mbH, 0-69451 Weinheim. 1997 0 0 0 5 -9 0 2~~9 7~0 3 0~-~3 1 1 $15.00+ .25/0

We report the development of dendritic siRNA nanostructures that are able to penetrate even difficult to transfect cells such as neurons with the help of a special receptor ligand. The nanoparticles elicit strong siRNA responses, despite the dendritic structure. An siRNA dendrimer directed against the crucial rabies virus (RABV) nucleoprotein (N protein) and phosphoprotein (P protein) allowed the suppression of the virus titer in neurons below the detection limit. The cell-penetrating siRNA dendrimers, which were assembled using click chemistry, open up new avenues toward finding novel molecules able to cure this deadly disease.

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