The parameter W a , which characterizes nuclear-spin-dependent parity violation (PV) in the molecular spinrotational Hamiltonian, was computed with a quasirelativistic Hartree-Fock approach for radium fluoride (RaF) and found to be one of the largest absolute values predicted so far. The peculiar electronic structure of RaF leads to highly diagonal Franck-Condon matrices between the energetically lowest two electronic states, which qualifies RaF for direct laser cooling. A subset of diatomic molecules with a wide range of internal structures suitable for this cooling technique is also indicated. As trapped cold molecules offer superior coherence times, RaF can be considered promising for high-precision experiments aimed at molecular PV.

Bijvoet's method, which makes use of anomalous x-ray diffraction or dispersion, is the standard means of directly determining the absolute (stereochemical) configuration of molecules, but it requires crystalline samples and often proves challenging in structures exclusively comprising light atoms. Herein, we demonstrate a mass spectrometry approach that directly images the absolute configuration of individual molecules in the gas phase by cold target recoil ion momentum spectroscopy after laser ionization-induced Coulomb explosion. This technique is applied to the prototypical chiral molecule bromochlorofluoromethane and the isotopically chiral methane derivative bromodichloromethane.

A program HOTFCHT for computing the vibronic fine structure of electronic spectra at different temperatures has been developed for a theoretical investigation of the temperature dependence of absorption and fluorescence spectra of organic molecules and a discussion of the temperature dependence of their photophysical properties. The program is based on the time-independent approach using the adiabatic and harmonic approximations. A Taylor series expansion of the electronic transition dipole moment takes into account vibronic coupling similar to a first-order Herzberg-Teller treatment. For the calculation of the Franck-Condon and Herzberg-Teller integrals, the recurrence formulae of Doktorov et al. (J. Mol. Spectrosc. 1977, 64, 302) were used while the derivatives of the electronic transition dipole moment were obtained numerically. As a first application of this program the vibronic fine structure of the S 0 -S 1 transitions of benzene and pyrazine were calculated at different temperatures. The equilibrium geometries and frequencies determined at the CASSCF level as well as the calculated spectra are in good agreement with experimental data; the main features of the spectra and especially "hot" bands are well-reproduced and can be assigned to the corresponding vibronic transitions.

In this work, rigorous prescreening conditions for the calculation of Franck-Condon factors (FCFs) are derived and implemented. These factors play an important role in numerous applications including the prediction and simulation of vibronic spectra, electron transfer rates, and nonradiative transition probabilities. For larger systems it is crucial to calculate only relevant FCFs, as the computational burden becomes otherwise prohibitive due to the sheer number of Franck-Condon integrals. By exploiting rigorous prescreening criteria one can significantly reduce the computational effort and systematically refine results to the desired target accuracy. In this work, such criteria are derived via the use of sum rules obtained through a coherent state generating function for the FCFs in the harmonic oscillator approximation, following the prescription of Doktorov et al. These sum rules allow efficient and rigorous prescreening prior to the calculation of entire batches of Franck-Condon integrals, reducing the subsequent computational burden. To illustrate the benefit of employing such conditions, they are applied in this work to calculate FC profiles for vibronic spectra of formic acid, thymine, anthracene, and a polycyclic aromatic hydrocarbon derivative containing about 450 vibrational degrees of freedom. Since the prescreening step gives stringent upper and lower bounds for the loss of FC intensity in these spectra arising from the neglected FCFs, the present approach renders most previous a priori selection schemes obsolete and has the potential to complement or even replace other approximate treatments.

We present a multiconfiguration linear response approach to electroweak quantum chemistry including effects from the parity violating weak nuclear force. Compared to our previous configuration interaction singles-restricted Hartree–Fock (CIS-RHF) approach [A. Bakasov, T. K. Ha, and M. Quack, J. Chem. Phys. 109, 7263 (1998)], the parity violating potential Epv is introduced by the linear response function and by solving the linear response equations in a direct iterative manner. Calculations are carried out within the multiconfiguration linear response approximation (MCLR) and its special cases, the configuration interaction approach (CI) and the random phase approximation (RPA). The systematic approach presented here, provides a systematic check and improvement upon various approximations used in the calculation of Epv. Extensive results are obtained for hydrogen peroxide at the CISDT (CI singles, doubles and triples) and CISDTQ (CI singles, doubles, triples, and quadruples) as well as at the complete active space self-consistent-field–linear response (CASSCF–LR) level. We compare to carlier results at the CIS-RHF level and confirm the order of magnitude increase in Epv reported earlier as compared to the widely used single determinant excitation-restricted Hartree–Fock (SDE-RHF) method. The new approach overcomes previous limitations for calculating Epv with biradicaloid structures such as twisted ethylene, for which numerical results are presented. This allows us to calculate Epv for a similar unsaturated system such as allene derivatives, which may be of experimental interest.