The laser magnetic resonance (LMR) spectroscopic technique has been used to reinvestigate the mid-infrared spectrum of the NCN free radical in its (3)Sigma(-)(g) ground electronic state. A liquid nitrogen-cooled carbon monoxide (CO) laser was used as a source of strong coherent radiation in the 1442-1484 cm(-1) region of the infrared. Vibration-rotation transitions were brought into resonance with the laser frequency using magnetic flux densities up to 1.4 T. Spectra were recorded in both parallel (Delta M-J = 0) and perpendicular (Delta M-J = +/- 1) polarizations with ten CO laser lines. Over one hundred new absorption lines were observed in the LMR spectra and have been subsequently assigned to transitions in either the 3(0)(1) fundamental band (near 1466.5 cm(-1)) or the 2(1)(1)3(0)(1) hot band (near 1455.6 cm(-1)) of NCN in the (3)Sigma(-)(g) ground state. An improved set of molecular parameters for NCN has been determined from a least-squares fit of all the available data on the infrared spectrum, provided by Fourier transform and LMR spectra. In the wake of an exhaustive analysis of the LMR spectra, several additional lines remain. Although chemical tests indicate these lines do not belong to NCN, it has not proved possible to identify their carrier(s).

A spectrometer based on a quantum cascade laser and capable of operating at particular wavelengths in the mid-infrared with very high sensitivity for the detection of open-shell molecules has been developed. It exploits magnetic field modulation in the Faraday rotation configuration. The signals for nitric oxide (NO) that may be observed with this instrument have been studied and their dependence on the J and Omega quantum numbers investigated with a simulation program. It is shown that the Q(3/2) transition of NO in the (2)Pi(3/2) component at 1875.8 cm(-1) would provide the greatest sensitivity for detection. The experimental observation of the R(21/2) transition of the Omega = 1/2 component gives a detection limit of 41 ppb of NO in air at a pressure of 25 mbar. Detection of NO through the Q(3/2) transition would provide a detection limit of 4 ppb at this pressure.

The infrared spectrum of the AsD radical in the X3Σ− ground state has been recorded using CO laser magnetic resonance. The radical was formed by the reaction between D atoms and arsenic powder. Low-N transitions in the fundamental band and in the (2–1) and (3–2) hot bands have been detected. Hyperfine structure from the 75As nucleus (I=3/2) is seen on many of the resonances. These measurements have been combined with information from previous measurements of rotational transitions at sub-millimeter wavelengths [H. Fujiwara, K. Kobayashi, H. Ozeki, S. Saito, A.I. Jaman, J. Chem. Soc. Faraday Trans. 93 (1997) 1045–1051] to determine an extended and improved set of molecular parameters for 75AsD. Comparison is made with corresponding parameter values for AsH.

Online sensing of nitric oxide traces based on a cw quantum cascade laser, operating near 5.2 μm, is reported. We utilized a Faraday modulation technique which provides unique selectivity since it exploits the magnetic moment of nitric oxide (NO) molecules. The minimum detectable NO concentration was found to be 4 ppb (sampling time: 10 s). Continuous monitoring of the NO release from nitrite solutions and human sweat samples is described. Detectable NO release rates are down to 10 pmol/s. We compare NO generation induced by a chemical, and by exposure to ultra-violet radiation.

Nitrite occurs ubiquitously in biological fluids such as blood and sweat, representing an oxidation product of nitric oxide. Nitrite has been associated with a variety of adverse effects such as mutagenicity, carcinogenesis, and toxicity. In contrast, here we demonstrate that the presence of nitrite, but not nitrate, during irradiation of endothelial cells in culture exerts a potent and concentration-dependent protection against UVA-induced apoptotic cell death. Protection is half-maximal at a concentration of 3 mM, and complete rescue is observed at 10 mM. Nitrite-mediated protection is mediated via inhibition of lipid peroxidation in a similar manner as seen with butylated hydroxytoluene, a known inhibitor of lipid peroxidation. Interestingly, nitrite-mediated protection is completely abolished by coincubation with the NO scavenger cPTIO. Using electron paramagnetic resonance (EPR) spectroscopy or Faraday modulation spectroscopy, we directly prove UVA-induced NO formation in solutions containing nitrite. In conclusion, evidence is presented that nitrite represents a protective agent against UVA-induced apoptosis due to photodecomposition of nitrite and subsequent formation of NO.

We report line width measurements of a quantum cascade distributed feedback laser by a heterodyne experiment. At currents slightly above threshold and a laser output power higher than 1 mW, the full width at half maximum of the beat signal was narrower than 0.5 MHz, which gives us an upper limit of the laser line width. As reference laser we used a carbon monoxide laser. Both lasers were operating unstabilized in continuous wave mode emitting light at about 5.2 μm.