Fermi resonance structure and femtosecond quantum dynamics of a chiral molecule from the analysis of vibrational overtone spectra of CHBrClF

Abstract

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.

Anharmonic resonances in the CH chromophore overtone spectra of CHBrF2

“…The discrepancies can be ascribed not only to additional local resonances not explicitly considered by the Hamiltonian employed in the present study, but also to the presence, in some integration ranges, of other bands. The magnitude of the deviations is comparable to that reported by other authors [24,26]. No significant differences between the values computed employing the fit with 12 degrees of freedom and those Table 2 we reports the value derived from the former.…”

“…In this case, the relative intensities are computed employing the following weighted average [26]: (12) where b and a are the indexes of the chromophore states having v 1 = N -1/2, v 2 = 1, v 7 = 0 and v 1 = N -1/2, v 2 = 0, v 7 = 1, respectively. The weighting factor f is given by the experimental intensity ratio of the first two components of the N = 3/2 polyad:…”

Analysis of an algebraic model for the chromophore vibrations of CF3CHFI

“…When frequencies are near resonant as ω s ≈ 2ω a ≈ 2ω b ≈ 2ω f a polyad naturally arises with many consequences. First we can write E 0 n = 2Pω b with the polyad P defined as P = n s + (n f + n a + n b )/2 (8) with the corresponding operator given asP by replacing n j →n j in Eq.8. Clearly all basis functions with n j giving the same value of P are degenerate.…”

“…The Hamiltonians reproduce and encode by their construction the experimental data [6,7,8,9,10,11,12]. In the mentioned examples the system is reducible to two degrees of freedom.…”

Synthetic routes for a variety of halogenated (chiral) acetic acids from diethyl malonate

“…[16][17][18] Here we focus on chiral halogenated acetic acids, 19 CXYZCOOH, which are of general interest in the elds mentioned above. They serve as precursors to halomethanes, specically CHBrClF, [20][21][22][23] CHBrFI, 24 and isotopically chiral CHDXY. [25][26][27][28] CHBrClF (7) itself has been subject to very early attempts to measure parity violation effects in molecules.…”