A novel photoacoustic (PA) system that uses a continuously tunable high-pressure CO(2) laser as radiation source is presented. A minimum detectable absorption coefficient of 10(-6) cm(-1) that is limited mainly by the desorption of absorbing species from the cell walls and by residual electromagnetic perturbation of the microphone electronics has currently been achieved. Although a linear dependence of the PA signal on the gas concentration has been observed over 4 orders of magnitude, the dependence on energy exhibits a nonlinear behavior owing to saturation effects in excellent agreement with a theoretical model. The calibration of the laser wavelength is performed by PA measurements on low-pressure CO(2) gas, resulting in an absolute accuracy of ± 10(-2) cm(-1). PA spectra are presented for carbon dioxide (CO(2)), ammonia (NH(3)), ozone (O(3)), ethylene (C(2)H(4)), methanol (CH(3)OH), ethanol (C(2)H(5)OH), and toluene (C(7)H(8)) in large parts of the laser emission range. The expected improvement in detection selectivity compared with that of studies with line-tunable CO(2) lasers is demonstrated with the aid of multicomponent trace-gas mixtures prepared with a gas-mixing unit. Good agreement is obtained between the known concentrations and the concentrations calculated on the basis of a fit with calibration spectra. Finally, the perspectives of the system concerning air analyses are discussed.

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The electronic and optical properties of DyP and DyBi are investigated both experimentally and computationally. The reflectivity spectra, which have been measured up to 12 eV on single crystals, display richly peaked spectral structures that are analogous for both pnictides. From the measured reflectivities the plasma frequencies, Drude relaxation times, and optical conductivity spectra are derived. The fitted Drude conductivity reveals that DyP and DyBi are semimetals with a number of free carriers of about 0.16 and 0.23 per formula unit, respectively. The very-structured experimental optical conductivity spectra are compared to calculated spectra, which are computed using two different approaches to the Dy 4 f states: the open-core approach and the L͑S͒DAϩU approach in three versions. These approaches to the 4 f states lead to very similar optical spectra. There exists a reasonable agreement between calculation and experiment for a number of the spectral features, which are interpreted by specific interband transitions within the calculated band structure. The agreement between theory and experiment substantiates that the 4 f electrons do not participate in the bonding. The differences that remain between theory and experiment for some of the spectral features do not appear to rest on aspects of the treatment of the 4 f states, but rather to be intrinsic shortcomings in the description of the other band states.

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We present a novel photoacoustic detection system with a high pressure CO2 laser as radiation source. The laser is continuously tunable across wavelength ranges from 13 cm-1 to 18 cm-1 wide. The narrow bandwidth of 0.017 cm-1 allows to resolve any fine structure in the absorption spectra of trace gases at atmospheric pressure. The absorption spectra of four gases are reported, demonstrating the great potential improvement in detection selectivity