We have determined the abundance of two different conformational structures of the mixed benzene dimer (C₆H₆)(C₆D₆) in a molecular beam, with various carrier gases. These two T-shaped conformers have a subtle zero-point energy difference of only a few cm^-1, and a transition state barrier of about 64 cm^-1. Nevertheless, depending on the carrier gas, the lowest energy conformer can exclusively be prepared in the molecular beam. Low-energy two-body collisions of the benzene-dimers with the carrier gas atoms are concluded to be responsible for this

We here present experimental infrared spectra on two (C6H6)(C6D6) benzene dimer isomers in the gas phase. The spectra show that the two benzene molecules in the dimer are symmetrically inequivalent and have distinct IR signatures. One of the two molecules is in a site of low symmetry, which leads to the IR activation of fundamental modes that are IR forbidden by symmetry in the monomer. In the spectra, all four fundamental C–H stretch modes of benzene are observed. Modes in the dimer are shifted up to 3cm−1 to the red, compared to the modes that are known for the monomer. For the ν13B1u C–H stretch fundamental mode of benzene, a first experimental value of 3015+2−5cm−1 is determined, in excellent agreement with anharmonic frequency calculations presented here.

We present three-dimensional microfluidic structures with integrated optical fibers, mirrors and electrodes for flow cytometric analysis of blood cells. Ultraprecision milling technique was used to fabricate different flow cells featuring single-stage and two-stage cascaded hydrodynamic focusing of particles by a sheath flow. Two dimensional focussing of the sample fluid was proven by fluorescence imaging in horizontal and vertical directions and found to agree satisfactorily with finite element calculations. Focussing of the sample stream down to 5 microm at a particle velocity of 3 m s(-1) is accessible while maintaining stable operation for sample flow rates of up to 20 microL min(-1). In addition to fluorescence imaging, the micro-flow cells were characterised by measurements of pulse shapes and pulse height distributions of monodisperse microspheres. We demonstrated practical use of the microstructures for cell differentiation employing light scatter to distinguish platelets and red blood cells. Furthermore, T-helper lymphocytes labelled by monoclonal antibodies were identified by measuring side scatter and fluorescence.

The experimental mid-and far-IR spectra of six conformers of phenylalanine in the gas phase are presented. The experimental spectra are compared to spectra calculated at the B3LYP and at the MP2 level. The differences between B3LYP and MP2 IR spectra are found to be small. The agreement between experiment and theory is generally found to be very good, however strong discrepancies exist when -NH 2 out-of-plane vibrations are involved. The relative energies of the minima as well as of some transition states connecting the minima are explored at the CCSD(T) level. Most transition states are found to be less than 2000 cm À1 above the lowest energy structure. A simple model to describe the observed conformer abundances based on quasiequilibria near the barriers is presented and it appears to describe the experimental observation reasonably well. In addition, the vibrations of one of the conformers are investigated using the correlation-corrected vibrational self-consistent field method.

No abstract