FERMI RESONANCE STRUCTURE AND FEMTOSECOND QUANTUM DYNAMICS OF A CHIRAL MOLECULE FROM THE ANALYSIS OF VIBRATIONAL OVERTONE SPECTRA OF CHBRCLF

The rovibrational spectra of bromochlorofluoromethane (CHBrClF) were m easured at intermediate (0.1 cm(-1) and high resolution (0.001 cm(-1)) between the far infrared (20 cm(-1)) and the visible range of the spe ctrum (14000 cm(-1)) by interferometric Fourier transform techniques a nd diode laser techniques in stationary samples and supersonic jets. A ll fundamentals and numerous combinations and overtone transitions cou ld be assigned and their band positions and integrated strengths were determined. A quantitative interpretation of the complex multiple reso nance structure of the CH chromophore spectra (about 50 assigned bands ) is given in terms of an effective anharmonic CH-stretching-bending H amiltonian and in terms of vibrational Variational calculations on a 3 -dimensional grid using ab initio (MP2 and B3LYP) and empirically adju sted potential hypersurfaces for the CH chromophore normal coordinate subspace. The systematic analysis of anharmonic resonances of the alky l CH chromophore in symmetric top (C-3v) and asymmetric top (C-s) mole cules is herewith extended to chiral molecules. We provide a detailed analysis of the chiral C-s symmetry breaking coupling in the effective Hamiltonian (coupling constant /k(sab)'/ similar or equal to (20+/-10 ) cm(-1)) and in the potential (C-sab and further terms) and their rel ationship. The implications for the femtosecond intramolecular dynamic s for CHBrClF are discussed in terms of quantum dynamical results for time-dependent populations, survival probabilities, wavepackets and al so time-dependent symmetries and their violations (formal a' and a '' species for vibrational C-s and l quantum number for vibrational C-inf inity v symmetry). We have also developed an improved synthesis of CHB rClF, which is suitable for the preparation of large quantities (sever al mel) of the pure (racemic) compound, and have demonstrated enantiom er separation by gas chromatography.