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The absorption spectra of the fundamental bands of the free radicals 10B16O and 11B16O in their ground 2Σ+ states have been measured in natural abundance and at Doppler limited resolution using diode laser spectroscopy. The band origins are found to be 1915.30674(14) and 1861.92409(13) cm−1, respectively. The rotational constants for the lower states are 1.877680(22) and 1.773421(10) cm−1, which are in excellent agreement with the microwave values for B0. Assuming a linear dependence of Bv on (v+1/2) the derived value of re is 1.204552(5) A˚. [Copyright &y& Elsevier]

Silane (SiH 4 ) plasmas are widely used for the deposition of hydrogenated amorphous silicon (a-Si:H) films. Nevertheless, the chemical processes governing film deposition are still incompletely understood. Moreover, there is still no general method available to determine the absolute concentration of the silyl radical (SiH 3 ), which is the accepted chemical precursor of a-Si:H films. In this study, a 10% silane in helium RF plasma was spectroscopically investigated between 2085 and 2175 cm -1 using an external cavity quantum cascade laser (EC-QCL) based spectrometer. This led to the identification of 4 distinct species from their absorption features: SiH 4 , disilane (Si 2 H 6 ), SiH 3 , and an unassigned short-lived species. Furthermore, 17 absorption features of SiH 3 were identified and unambiguously assigned. Fast spectral scanning of selected absorption features belonging to the four species in a 10 Hz pulsed RF plasma enabled the measurement and interpretation of their temporal behavior in terms of plausible chemical reactions involving silicon containing species. By quantitatively measuring the decay of the SiH 3 a ← a p P 4 (5) transition at 2151.3207 cm -1 after the discharge was stopped, its line strength (S) was determined to be (7.5 ± 5.5) × 10 -20 cm 2 cm -1 mol -1 .

Sensitive trace gas detection plays an important role in current challenges occurring in areas such as industrial process control and environmental monitoring. In particular, for medical breath analysis and for the detection of illegal substances, e.g., drugs and explosives, a selective and sensitive detection of trace gases in real-time is required. We report on a compact and transportable multi-component system (RES-Q-Trace) for molecular trace gas detection based on cavity-enhanced techniques in the mid-infrared (MIR). The RES-Q-Trace system can operate four independent continuous wave quantum or interband cascade lasers each combined with an optical cavity. Twice the method of off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) was used, twice the method of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS), respectively. Multi-functional software has been implemented (i) for the general system control; (ii) to drive the four different laser sources and (iii) to analyze the detector signals for concentration determination of several molecular species. For the validation of the versatility and the performance of the RES-Q-Trace instrument the species NO, N₂O, CH₄, C₂H₄ and C₃H₆O, with relevance in the fields of breath gas analysis and the detection of explosives have been monitored in the MIR with detection limits at atmospheric pressure in the ppb and ppt range ., Competing Interests: The authors declare no conflict of interest.

We report on sensitive detection of atmospheric methane employing quantum cascade laser based optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS). An instrument has been built utilizing a continuous-wave distributed feedback quantum cascade laser (cw-QCL) with a V-shaped cavity, a common arrangement that reduces feedback to the laser from non-resonant reflections. The spectrometer has a noise equivalent absorption coefficient of 3.6 × 10 -9 cm -1 Hz -1 / 2 for a spectral scan of CH 4 at 7.39 μm. From an Allan-Werle analysis a detection limit of 39 parts per trillion of CH 4 at atmospheric pressure within 50 s acquisition time was found.

The recent availability of thermoelectrically cooled pulsed and continuous wave quantum and inter-band cascade lasers in the mid-infrared spectral region has led to significant improvements and new developments in chemical sensing techniques using in-situ laser absorption spectroscopy for plasma diagnostic purposes. The aim of this article is therefore two-fold: (i) to summarize the challenges which arise in the application of quantum cascade lasers in such environments, and, (ii) to provide an overview of recent spectroscopic results (encompassing cavity enhanced methods) obtained in different kinds of plasma used in both research and industry.

The line strengths of five Q-branch lines of the first hot band of the out-of-plane bending vibration (2(1)(2)) of the methyl radical, CH 3, have been measured using infrared laser absorption spectroscopy. The spectra of the radical were measured in situ in a microwave discharge using ditertiary butyl peroxide, diluted in argon as the precursor. The line strengths were used to determine the transition dipole moment of the hot band. Absolute concentrations of the radical were required for this purpose, and these were determined kinetically from the measured decays of the spectral lines after the discharge was extinguished. The translational, rotational, and vibrational temperatures were also determined spectroscopically from measured integrated line intensities and line widths. The transition dipole moment of the first hot band was determined to be 0.31(6) D. This value is in satisfactory agreement with the value of 0.27(3) D from a high-precision ab initio calculation using the self-consistent electron pairs (SCEP) method reported by Botschwina, Flesch, and Meyer [Botschwina, P.; Flesch, J.; Meyer, W. Chem. Phys. 1983, 74, 321].