Pressure broadening coefficients for the following NO transitions were measured at room temperature using NO, N2, Ar, He as collisional partner: 14N16O: 1/2 R(1/2), 1/2 P(3/2), 1/2 R(9/2), 3/2 R(9/2), 1/2 P(17/2); 15N16O: 1/2 R(21/2), 3/2 R(21/2), 3/2 R(19/2). We used a tunable spin-flip Raman-laser spectrometer and two different techniques, conventional absorption spectroscopy and Zeeman Modulation spectroscopy. The results obtained with both techniques agree within the error limits. The results are compared with previously published values.

Two separate studies of the CD radical in vibrationally excited levels of its X2Π ground state have been made by the technique of laser magnetic resonance. The first of these studies was in the far-infrared; rotational transitions of CD in the v=1 and 2 levels have been detected. The second study was carried out in the mid-infrared using a carbon monoxide laser magnetic resonance spectrometer. In these experiments, transitions in the (1,0), (2,1), and (3,2) bands have been detected. All the available data on CD in its X2Π state have been used to determine an improved set of molecular parameters for the CD radical. In addition to the above data sets, previous far-infrared laser magnetic resonance on the CD radical in the v=0 level and FTIR observations of the (1,0) and (2,1) bands have been included. The principal molecular parameters determined are: ν0=2032.03360(18)cm-1, ωexe=34.72785(58)cm-1, B0=7.7018632(14)cm-1, αB=-αe=-0.212239(11)cm-1, where the figures given in parentheses are one standard deviation from the least squares fit. A small but significant dependence of the orbital contribution to the magnetic dipole moment on the vibrational quantum number is detected. This may reflect the mixing between the X2Π and a4Σ- states of CD.

Nitric oxide (NO) is commonly thought to reveal more precise values of pulmonary gas uptake through alveolar-capillary membranes (DL) than the normally used carbon monoxide (CO). Since such measurements are influenced by a significant endogenous NO delivery within human airways, we propose the use of the naturally occurring (15)N-labelled stable nitric oxide isotope (15)NO. It occurs with a relative abundance of 0.37% of the dominating isotope (14)NO. Therefore, the endogenous (15)NO production can be neglected. In the present pilot study we demonstrate the workability of (15)NO in determining DL in healthy individuals. In seven female and 15 male volunteers, averaged values of DL increase with increasing mean alveolar volume as well as individual body height ( P=0.000001). Due to the very high significance level obtained from the multiple regression analysis, we conclude that the application of (15)NO establishes a novel approach to calculate standard values of DL. Such calculations can be employed to predict a reference for patients who suffer from pulmonary diffusion limitation.

Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was operated at liquid nitrogen temperature near λ=5.2 μm. In the first configuration, a 100 m optical path length multi-pass cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy (CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb when using CES. The two techniques are compared, and potential future developments are discussed.

We present an ultrahigh-resolution saturation spectrometer based on a line-tunable carbon monoxide laser near 60 THz (lambda = 5 microm). A spectral resolution of 14 kHz (Dnu/nu = 2.3 x 10(-10)) for CO fundamental-band transitions was achieved, which improves on earlier results by one order of magnitude. A frequency-locking scheme using tunable microwave sidebands provides tunability and absolute frequency control of the CO laser on the kilohertz. Transit-time broadening and pressure broadening of the observed transitions are significantly reduced by use of expanded laser beams in a 24-m absorption cell at pressures down to 0.0 1Pa. The new spectrometer is suitable for the study of saturation line shapes and the development of a new generation of frequency standards in the 60-THz region.

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.

We report on infrared laser spectroscopic measurements of the isotopic composition of methane (12CH4, 13CH4) in natural air samples with a cavity ring-down technique. A CO overtone sideband laser is utilized to excite a high-finesse cavity which provides an effective optical absorption path length of 3.6 km. We achieved a detection limit of 105 ppt methane in ambient air using an integration time of 20 s. This corresponds to a minimum detectable absorption of 1.9×10-9 /cm. Rapid determination of the 13C/12Cisotopic ratio of methane in ambient air without sample preconcentration or gas processing is realized. The present system requires only few minutes for an isotopic ratio measurement with a precision of 11%o .

Isoprene (C5H8) is one of the most important biogenic volatile organic compounds (VOCs) in the atmosphere. To calculate the impact of isoprene on atmospheric processes models have been developed that describe the isoprene release from plants. Measurements of this release require techniques for a fast, sensitive, on-line isoprene detection.

We report on spectroscopic real-time detection of (13)CH(4) in ambient air. Our measurements were carried out by means of cavity leak-out absorption spectroscopy employing a tunable cw laser in the mid-infrared spectral region near lambda = 3 microm. A CO laser in combination with tunable microwave sideband generation was used as the light source. Using a 50-cm-long ringdown cell with R = 99.98% mirrors, we achieved a detection limit of 290 parts in 10(12) (ppt) (13)CH(4) in ambient air (integration time, 100 s). The corresponding noise-equivalent absorption coefficient was 5 x 10(-9)/cm.

The emission of the tropospheric trace gas acetaldehyde was determined in leaves of 4-month-old poplar trees (Populus tremula x P. alba) grown under controlled environmental conditions in a greenhouse. Using a dynamic cuvette system together with a high sensitivity laser-based photoacoustic detection unit, rates of acetaldehyde emission were measured with the high time resolution of about 15 min. Submergence of the roots resulted in the emission of acetaldehyde by the leaves. The emission increased linearly before reaching more or less steady-state values (ca 350 nmol m (- 2) min (- 1); ca 470 ng g (- 1) dry weight min (- 1)) after approximately 6 h. Prolonged flooding of poplar trees resulted in a clear diurnal rhythm of acetaldehyde emission, The emission rates decreased when the light was switched off in the evening and peaked in the morning after the light was turned on again. This pattern significantly correlated with diurnal rhythms of stomatal conductance, photosynthesis, transpiration and with the concentrations of ethanol, the assumed precursor of acetaldehyde, in the xylem sap of flooded poplar trees. It may be concluded that under conditions of diminished stomatal conductance, acetaldehyde emission declines because its diffusive flux is reduced. Alternatively, reduced transpiration may decrease ethanol transport from the roots to the shoots and appreciable amounts of the acetaldehyde precursor ethanol are lacking in the leaves. The present results support the view that acetaldehyde emitted by the leaves of plants is derived from ethanol produced by alcoholic fermentation in submerged roots and transported to the leaves with the transpiration stream.

By using tunable microwave sidebands added to CO-laser lines, we have made more sub-Doppler heterodyne frequency measurements on OCS. Three new rotational transitions have been measured for each of three absorption bands, 1000–0000, 0201–0000, and 0311–0110. The absolute uncertainties of the measurements are on the order of ±25 kHz. New calibration tables are given for the region 1860–1925 and 2020–2085 cm−1 based on the most recent OCS measurements.

We have set up a new CO-laser sideband spectrometer for high-resolution molecular-beam optothermal spectroscopy in the mid infrared. By mixing CO-laser lines with tunable microwave radiation, a spectral coverage of about 50% is achieved. Using a microwave resonator, a typical output power of 3 mW is realized in the region of 5–6.6 μm (1500–2000 cm−1). The resolution in our molecular-beam apparatus with optothermal detection is 2.8 MHz (full width at half maximum). The new setup allowed the observation of the first high-resolution rotationally resolved spectrum of formic acid dimer (HCOOH)2.

Saturated absorption lineshapes in the CO v = 1 <-- 0 band were measured at pressures between 10(-2) Pa and 10(2) Pa in pure CO and CO-He mixtures with a spectral resolution of better than Delta nu/nu = 3 x 10(-10). The CO saturation signals mainly consist of narrow dips with a homogeneous width that nonlinearly depends on pressure due to dominant contributions of velocity changing collisions (VCC) and a broader background that can also be attributed to VCC. Preliminary evaluation shows a change of the CO self broadening coefficient from 96 kHz/Pa for p < 3 Pa to 38 kHz/Pa for 15 Pa < p < 40 Pa. The GO-He broadening coefficient was found to be 47 kHz/Pa for 0.2 Pa < p < 16 Pa.

ABSTRACTEthylene emission from wild‐type Agrobacterium tumefaciens (C58)‐induced stem tumours of Ricinus communis was continuously measured with two different methods, process gas chromatography and photo‐acoustic spectrometry. Ethylene production was as high as 700 pmol g FW–1 h–1, namely 140 times greater than emitted by non‐tumourized control stems. It was highest in 5‐week‐old tumours, independent of light, depressed by anoxia and, during water deficit it was stimulated by rewatering. A remarkable concomitant CO‐production was discovered. Accumulation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), the substrate of ACC‐oxidase, preceded ethylene emission with a maximum 2 weeks after tumour induction. Simultaneously, the xylem in the tumour‐adjacent host stem underwent drastic changes: it increased two to three times in thickness, vessel diameters decreased, the rays remained unlignified and became multiseriate. With increasing emission of ethylene aerenchyma developed in the non‐transformed, tumour‐surrounding tissue that formerly was stem cortex. Cotyledons reacted with epinastic symptoms indicating induction of senescence. The present results reveal an important role of ethylene, in addition to cytokinin and auxin, for the differentiation and physiology of A. tumefaciens‐induced tumours.

laser. After excitation, the laser power is turned off for a short time and the subsequent decay of the radiation stored in the cavity is observed via detection of the light leaking out through one of the cavity mirrors. Measurement of the decay time allows one to determine the photon losses und thus to detect weakly absorbing species inside the cavity. Since the cavity is frequency-locked to the laser the decay time can be probed with a high repetition rate, basically limited by the sampling rate of the analog-to-digital converter. This approach is closely related to cavity ring-down spectroscopy with pulsed lasers, but exhibits several advantages concerning spectral resolution and detection sensitivity. As a practical example we demonstrate monitoring of trace amounts of ethylene. Using R=99.5% mirrors we achieve a detection limit of 1 ppb ethylene (integration time: 100 s) corresponding to absorption losses of 3×10-8 /cm. Further improvement is feasible when mirrors with higher reflectivity become available.

Laser magnetic resonance spectroscopy (LMRS) is a sensitive and isotope-selective technique for determining low concentrations of gaseous free radicals with high time resolution. We used this technique to analyze the nitric oxide (NO) concentration profile while simultaneously measuring the flow and expired volume during several single breathing cycles. Eight healthy, nonallergic volunteers were investigated. An initial NO peak was found in all breathing cycles before the NO concentration dropped to a relatively stable plateau in the late phase of expiration. The nasal NO peak was significantly higher than the oral NO peak. The nasal NO plateau was always higher than the oral NO plateau. The height of the initial nasal and oral NO peak rose with increasing duration of breath hold, whereas the late expiratory NO plateau changed only little for either the nasal or the oral breathing cycles. Our findings demonstrate, in line with other reports using other techniques, that the nose is the primary source for NO within the airways.

We report on our recent advances with cavity ring-down spectroscopy using mid-infrared cw lasers. An external high- finesse cavity is excited on a single fundamental mode with a tunable laser operating in the 3 micrometers region. After excitation the laser power is turned off for a short time and the subsequent decay of the field stored inside the cavity is observed. The effective pathlength covered by the laser light inside the cavity during the decay amounts to several km, depending on the mirror reflectivity. Measurement of the decay time gives the photon losses and thus enables the detection of weakly absorbing species inside the cavity. This approach is closely related to cavity ring-down spectroscopy with pulsed lasers. However the cw approach exhibits several advantages concerning spectral resolution and detection sensitivity. Application of this method to online monitoring of trace gases seems to be very promising. We demonstrate detection of hydrocarbons, like membrane and ethylene on the ppb level.

Continuous-wave optical parametric oscillators (OPO) emerge as new powerful sources for broadly tunable infrared radiation. Based on periodically poled Lithium Niobate (PPLN) a singly-resonant OPO (SRO) with pump enhancement delivers idler radiation of about 100 mW between 3 and 4 mu m. Here it is applied for photoacoustic trace gas detection. The free idler wavelength selection allows one to use the strongest absorption features for the molecules under study. Ethane and methane an detected at 3.34 mu m and 3.26 mu m with detection limits of 0.46 and 0.26 ppb, respectively. Ethylene was detected with 4 ppb at 3.35 mu m. This new compact source opens great opportunities for the development of transportable photoacoustic detectors.

H6) at 3.34 μm using a widely tunable cw single-frequency optical parametric oscillator. The high frequency and power stability and the continuous tunability of the parametric oscillator make it ideally suited for this application. Detection sensitivities of 0.5 ppb for ethane are obtained, which is comparable to the best results previously obtained with intracavity detection using line-tunable CO overtone lasers. The flexibility and compact size of cw single-frequency parametric oscillators can lead to portable photoacoustic trace-gas detection systems for environmental monitoring and process control.