Ab initio investigation of the laser induced desorption of iodine from KI(100)

Based on potential–energy curves that were derived from ab initio calculations within the framework of many-body perturbation theory, mixed quantum–classical simulations have been performed to understand the dynamics of the photodesorption process of iodine from KI(100). Dissipation and recoil processes were included by adding a surface oscillator to the ab initio potentials. Using this approach, we reproduce and explain qualitatively the desorption spectrum and the kinetic energy distribution of the desorbing iodine. PACS  68.43.Bc; 31.15.Qg; 31.50.Gh     

Continuous wave optical parametric oscillator for quartz-enhanced photoacoustic trace gas sensing

A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy (QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm^-1 and continuous spectral coverage exceeding 16.5 cm^-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning range and locking of the idler wavelength with a stability of 1.7×10^-3 cm^-1 over at least 30 min. Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption coefficient of 4.4×10^-7 cm^-1  W/Hz^1/2. PACS 42.55.Wd; 42.65.Yj; 42.62.Fi     

Small 51V chemical shift anisotropy for LaVO4 from MQMAS and MAS NMR spectroscopy

51V MQMAS NMR of the triple-quantum transitions is shown to be particularly useful in the determination of the sign and magnitude of the chemical shift anisotropy (CSA) parameter delta(sigma)(= delta(iso)-delta(zz)) along with the asymmetry parameter (eta(sigma)) for a vanadium environment with a small CSA and a rather strong quadrupole coupling. This is demonstrated for the orthovanadate LaVO(4) for which 51V magic-angle spinning (MAS) NMR of the central and satellite transitions at 14.1T gives precise values for the quadrupole coupling parameters, however, an ambiguous sign for delta(sigma). The CSA parameters are reliably obtained from analysis of the spinning sidebands observed in a 51V triple-quantum MAS experiment. Combining these data with least-squares analysis of the manifold of spinning sidebands in the single-pulse MAS NMR spectrum results in a precise determination of the magnitudes and relative orientation of the 51V quadrupole coupling and CSA tensors for LaVO(4).     

Sensitive amplitude-and phase-modulated absorption-spectroscopy with a continuously tunable diode laser

The output beam of a continuously tunable GaA1As-diode laser with external cavity is phase-modulated at 800 MHz in an electrooptic LiTaO₃ crystal. The amplitude of the rf voltage applied to the EOM is modulated at 80 kHz in order to allow lock-in detection. Using a multipass absorption cell the detection limit of the absorption coefficient α could be pushed down to α_min ≧2 × 10^?10 cm^2212;1. The sensitivity of the techique is demonstrated by examples of overtone transitions in C₂H₂ and H₂O vapor.     

Über synthesen von difluoraminopyrimidinen

The syntheses of difluoroaminopyrimidines are reported. By direct fluorination of amino derivatives the corresponding difluoroamino-compounds and other fluorinated products are formed. In the case of the alkylation of difluoroamine by protonated pyrimidines the formation of difluoroamino-compounds is discussed.