CO Overtone Research Articles

Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star

We report on the detection and analysis of hot ro-vibrational H2O emission from SVS-13, a young stellar object previously known to have strong CO overtone bandhead emission. Modeling of the high-resolution infrared spectrum shows that the H2O emission is characterized by temperatures ~ 1500 K, significantly lower than the temperatures that characterize the CO bandhead emission. The widths for the H2O lines are also found to be smaller than those for the CO lines. We construct a disk model for the emission that reproduces the CO and H2O spectrum. In this model, the H2O lines originate at somewhat larger disk radii (<= 0.3 AU) than the CO overtone lines (<= 0.1 AU). We find that the H2O abundance is about a factor of 10 lower than the calculated chemical equilibrium abundance. Large, approximately transonic, local line broadening is required to fit the profile of the CO bandhead. If this velocity dispersion is identified with turbulence, it is of significant interest regarding the transport of angular momentum in disks. Large local broadening is also required in modeling CO overtone emission from other young stellar objects, suggesting that large turbulent velocities may be characteristic of the upper atmospheres of the inner disks of young stars.

Two Embedded Young Stellar Objects in NGC 2264 with FU Orionis Characteristics

We report the discovery of two young stars in the NGC 2264 star-forming molecular cloud whose physical and morphological characteristics are similar to FU Orionis objects. The objects form a close pair and exhibit a curved reflection nebula in the near-IR. The brighter of the two stars, AR 6A, is optically visible but considerably reddened, has a small 3 μm IR excess, shows pronounced 2.294 μm CO overtone band head absorption, and is the brightest near-IR object in the region. The fainter star, AR 6B, located 28 south, has a much larger thermal IR excess and shows considerably deeper CO band head absorption identical to that seen in several known FU Orionis stars (FUors). Both stars therefore resemble FUors in terms of thermal excess, near-IR spectral features, and morphology. Here we discuss the characteristics of AR 6A and AR 6B in relation to the FUor population and propose that both stars are likely additional members of this class of young stellar outburst objects. We speculate that the simultaneous appearance of two FUor–like objects in a binary system, which would be highly unlikely if unrelated, could be caused by orbital evolution in a newly formed hierarchical quadruple system.

Sensitivity of molecular vibrational dynamics to energy exchange rateconstants

The sensitivity of molecular vibrational population dynamics, governing the COlaser operated in fundamental and overtone transitions, to vibration-to-vibrationrate constants is investigated. With this aim, three rate constant sets have beenused, differing in their completeness (i.e. accounting for single-quantumexchange only, or for multi-quantum exchange with a limited number of rateconstants obtained by semiclassical calculations, and, finally, with anexhaustive set of rate constants including asymmetric exchange processes,as well) and in the employed interaction potential. The most completeset among these three is introduced in this paper. An existing earlierkinetic model was updated to include the latter new data. Comparison ofdata produced by kinetic modelling with the above mentioned sets ofrate constants shows that the vibrational distribution function, and, inparticular, the CO overtone laser characteristics, are very sensitive to thechoice of the model. The most complete model predicts slower evolution ofthe vibrational distribution, in qualitative agreement with experiments.

On the massive star contents of Cygnus OB2

We present a near-infrared spectroscopic survey of a large area centered on the Cygnus OB2 association aimed at constraining its massive star contents. Our goal is to establish a nearly complete list of O-type members of the association, both to examine recent claims based on starcounts that suggest a richer content than previously thought, and to provide a suitable database for further studies of the entire high-mass end of one of the richest associations of the Galaxy. The target selection is based on the JHK photometry published in the 2MASS all-sky survey. We identify 46 new early-type candidates, most of them expected to be O-type stars, plus 16 new stars with emission in Br and often in other lines as well, characteristic of evolved massive stars undergoing intense mass loss. We also present spectra of three luminous stars with CO overtone emission, one of them having also intense H2 emission and being associated with compact nebulosity. By considering our ndings, those of other authors, and plausible completeness corrections, we estimate the number of O-type stars or stars having evolved from a O-type progenitor to be 90{100, slightly below, but compatible with, most recent starcounts estimates by Knodlseder (2000, A&A, 360, 539). These results support the notion that Cygnus OB2 may be considered as a young globular cluster. The lists of new members that we provide, in particular those with emission lines, should be a useful resource for future investigations of Cygnus OB2 itself, as well as of very massive stellar evolution by providing a nearby, abundant sample of stars sharing a common environment.

Pulsed laser operating on the first vibrational overtone of the CO molecule in the 2.5 — 4.2-μm range: 3. The gain and kinetic processes on high vibrational levels

The gain dynamics in the active medium of an overtone CO laser operating on the transitions between high vibrational levels is studied experimentally and theoretically. The gain dynamics is measured on the vibration — rotation transitions of the CO molecule [the P(12) spectral line in the vibrational bands from 20 → 18 to 36 → 34] in CO — He and CO — N2 laser mixtures. The maximum small-signal gain was 0.43 m-1. The theoretical model of the CO laser was significantly improved. It was shown that multiquantum and asymmetric VV-exchange processes should be included in the analysis of the population dynamics of high vibrational levels of the CO molecule.

Atmospheric trace gas analysis with cavity ring‐down spectroscopy

AbstractCavity ring‐down spectroscopy (CRDS) is a highly sensitive laser absorption method. It can be used for quantitative analysis of molecular species at the sub‐ppb level. The absorption cell (cavity) is sealed by two high‐reflective mirrors on each side, which results in an effective absorption path‐length of some kilometers. Our experiments for atmospheric gas analysis have been carried out so far with an Excimer pumped dye laser in the UV‐VIS and a CO overtone sideband laser in the wavelength region around 3 μm. Experiments with an all solid‐state difference frequency laser system will follow. In the UV‐VIS region, we measured trace gas molecules like SO2, NO2, and CH2O. In the mid‐infrared, around 3 μm, we measured hydrocarbons like CH4, C2H6, and C2H4 with a detection limit of less than 1 ppb. The noise equivalent absorption coefficients in the MIR are in the order of 1.7·10−9 cm−1. Due to the high data acquisition rate and the high sensitivity, CRDS enables real‐time detection of trace gases in ambient air.

Real-time monitoring of ethane in human breath using mid-infrared cavity leak-out spectroscopy

We report on spectroscopic real-time analysis of ethane traces in exhaled human breath. Ethane is considered the most important volatile marker of free-radical induced lipid peroxidation and cell damage in the human body. Our measurements were carried out by means of mid-infrared cavity leak-out spectroscopy in the 3 μm region, a cw variant of cavity ring-down spectroscopy. The spectrometer is based on a CO overtone laser with tunable microwave sidebands. The resulting system proved to be an unique tool with high sensitivity and selectivity for rapid and precise breath testing. With a 5 s integration time, we achieved a detection limit on the order of 100 parts per trillion ethane in human breath. Thus, sample preconcentration is unnecessary. Time-resolved monitoring of the decaying ethane fraction in breath after smoking a cigarette is demonstrated.

Isotopic ratio measurement of methane in ambient air using mid-infrared cavity leak-out spectroscopy

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 .

Pulsed laser operating on the first overtone of the CO molecule in the 2.5–4.2-μm range. II. Frequency-selective lasing

Lasing properties of a pulsed electroionisation CO laser operating on the first overtone of the CO molecule in the frequency-selective regime were studied experimentally and theoretically. Lasing was observed on a large number of separate vibrational-rotational transitions ν+2→ν from 13→11 to 38→36 (more than 400 spectral lines) in the spectral range from 2.7 to 4.2 μm. The specific output energy of the overtone CO laser reached ~3.0 J l-1 amagat-1, and the electrooptical conversion was ~0.6 %. The formation of emission spectra from high vibrational levels in the overtone CO laser observed for the first time is discussed. The comparison of experimental and theoretical data showed the necessity of including the multiquantum exchange on high vibrational levels into the kinetic model of the active medium of the CO laser.

Pulsed laser operating on the first vibrational overtone of the CO molecule in the 2.5–4.2-μm range: 1. Multifrequency lasing

Characteristics of a pulsed, multifrequency electroionisation CO laser operating on the first vibrational overtone of the CO molecule are studied experimentally and theoretically. It is shown experimentally that a pulsed, multifrequency overtone CO laser is an efficient source of coherent radiation in the 2.5–4.1-μm region whose specific output reaches 50 J l-1 amagat-1 and the electro-optical efficiency amounts to 11 %. A theoretical analysis based on experimental data shows the feasibility of obtaining overtone emission with efficiency as high as ~20 %. The alternation of the intensity of vibrational bands in the overtone CO laser is discussed. This effect is caused by the cascade mechanism of formation of the emission spectrum. The comparison of experimental data with calculations showed that they agree well with respect to spectral and energy characteristics of the overtone CO laser. Moreover, it revealed the necessity of refinement of the kinetic model of the active medium of the CO laser for obtaining an adequate description of time parameters of a laser pulse.

Frequency-tunable optically pumped carbon monoxide laser

Single-line frequency-tunable lasing was observed in an optically pumped, repetitively pulsed, room-temperature CO laser for the first time. The R(0) and R(7) ro-vibrational transitions in the (2,0) overtone of CO at 2.3 /spl mu/m were optically pumped with a high-energy optical parametric oscillator. Single-line lasing was observed on (2,1) P(2)-P(17) transitions and R(0)-R(11) transitions (covering wavelengths within the range 4.6-4.9 /spl mu/m) when using a diffraction grating as the spectrally selective reflector of the laser resonator. The observed CO laser pulse lengths were /spl sim/10/sup -7/ s with peak power up to 10/sup 4/ W. The influence of CO pressure, the addition of buffer gas (He, Ar), Q-factor of the laser resonator, and the pump pulse energy on CO laser pulse temporal characteristics and output energy spectral distribution was studied experimentally.

Responses of the infrared sensilla of Melanophila acuminata (Coleoptera: Buprestidae) to monochromatic infrared stimulation.

The pit organs of the beetle Melanophila acuminata were stimulated with monochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity was in the wavelength range 2.8-3.5 micron. In this range a stimulus intensity of 14.7 mW cm(-2) was sufficient to generate single action potentials. At a wavelength of 5 microm receptor performance significantly decreased. An increase in stimulus intensity caused a decrease in response latency and an increase in the number of action potentials elicited. At a given wavelength (3.4 microm) the dynamic amplitude range of action potential responses covered 12 dB. At high stimulus intensities (94.2 mW cm(-2)) a stimulus duration of 4 ms was sufficient to generate one to two action potentials and a stimulus duration of 60 ms already caused response saturation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials were visible up to a frequency of 600 Hz.

On-line monitoring of biogenic isoprene emissions using photoacoustic spectroscopy

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. Photoacoustic (PA) spectroscopy is applied here for the first time to monitor biogenic isoprene emissions. A CO overtone PA spectrometer is used for the detection, probing the C-H stretching vibrations in the 3 to 4 μm range. This allows us to detect isoprene down to a few ppb with a time resolution of one minute in a continuous gas flow. The number of laser lines can be adjusted to meet the requirements of the respective experiment in terms of time resolution and selectivity against other possibly interfering VOCs. This results in a highly versatile instrument for the isoprene detection in biological experiments. Furthermore, the infrared fingerprint offers the potential to detect different isoprene isotopomers simultaneously, thus allowing us to carry out on-line labelling experiments. The new apparatus was used to study the light dependence of isoprene emission from Eucalyptus globulus. The results demonstrate, that the detector system is a promising tool for the study of plant gas emissions. It allows the validation of existing emission models which are important for atmospheric processes.

Imaging of CO and CO 2 using infrared planar laser-induced fluorescence

Infrared (IR) planar laser-induced fluorescence (PLIF) techniques for imaging of carbon monoxide and carbon dioxide are reported. These diagnostics employ a tunable IR source to excite overtone and combination band transitions of CO and CO 2 , respectively, and one or two InSb focal plane arrays to collect fluorescence emitted via fundamental transitions from excited vibrational states. A brief outline of the theoretical framework for absorption and fluorescence modeling is presented, with most attention paid to the distinct characteristics stemming from the use of vibrational (IR) transitions as compared to more traditional electronic (UV) transitions. Of note are the conclusions that (1) acceptable fluorescence quantum yield (and therefore signal level) can be achieved despite relatively small Einstein A coefficients, as the quenching processes following IR excitation are often slow: and (2) vibration-to-vibration transfer to other IR-active species can enble imaging of more than one species with a single excitation wavelength. Experimentally, the large dynamic range afforded by the IR cameras (14 bit) allows for effective imaging despite the presence of background luminosity, while the use of two cameras enables imaging of multiple species simultaneously and/or common-mode rejection of luminous background in unsteady flows. PLIF imaging of CO and CO 2 is demonstrated for room-temperature mixing processes with signal-to-noise ratio=1 detection limits near 1000 ppm. Imaging of both CO and CO 2 in a steady laminar coflowing CO/Ar/H 2 flame is also presented using laser excitation of CO only.

Sub-Doppler Heterodyne Frequency Measurements on OCS Near 2900 cm−1Using a CO Overtone Sideband Spectrometer

We present sub-Doppler heterodyne frequency measurements on 10 rovibrational transitions of carbonyl sulfide (OCS) between 2894 and 2910 cm−1. The measurements were made using a CO overtone laser which had limited tuneability through the generation of microwave sidebands in a CdTe crystal. With this technique the laser frequencies were shifted to the desired OCS transition frequencies. The transition frequencies could be measured with uncertainties less than 30 kHz (Δν/ν = 3 × 10−10) by frequency offset-locking the CO overtone laser to combination frequencies of two saturation-stabilized CO2laser standards. The measured transition frequencies of OCS were combined with previous sub-Doppler, Fourier transform, and microwave measurements to recalculate improved calibration tables for the 1001–0000, 111e1–011e0, and 111f1–011f0 bands. These tables are suitable for the calibration of infrared spectrometers in the 87 THz region (near 2900 cm−1).

Faraday Laser Magnetic Resonance Spectroscopy of Vibrationally Excited C2D

We studied the gas phase spectrum of the deuterated ethynyl radical C2D in the region between 3196 and 3243 cm−1using a Faraday LMR spectrometer in combination with a CO overtone laser. The C2D radicals were generated in a dc glow discharge containing helium, deuterium, and acetylene. We observed a hot band between two vibronic2Π states with an origin at 3225 cm−1. The lower level is assigned to the first excited bending level of the electronicXground state. The upper level corresponds to the first excited electronic stateAat 3513 cm−1, which was observed previously [J. Mol. Struct.190,41–60 (1988)]. This region is subject to strong vibronic interaction, caused by mixing of the electronicXground state with theAstate at 3513 cm−1. From the analysis of the spectra we could determine the orbitalgfactor of the upper level, which gave important information about the mixing ratios. In addition we were able to derive a precise term value for the first excited bending level of the electronicXground state. The experimentally derived molecular parameters are compared with theoretically calculated values, obtained byab initiocalculations.

Photoacoustic trace-gas detection using a cw single-frequency parametric oscillator

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.

Tunable carbon monoxide overtone laser sideband system for precision spectroscopy from 26 to 41 µm

We report a source of tunable laser radiation for high-precision molecular spectroscopy in the 2.6- 4.1-microm spectral region. Laser light from a CO overtone laser is mixed with microwaves, generating tunable sidebands of ~1 mW of power. We achieve very high absolute frequency accuracy by frequency-offset locking the CO laser to a CO(2) laser secondary frequency standard. The uncertainty of the laser frequency is less than 30 kHz (Dnu/nu=3x10(-10)) , and the laser linewidth is of the order of 100 kHz. This tunable and ultrastable laser system is suitable for very accurate molecular spectroscopy and metrology in a most interesting wavelength region. We demonstrate an application of the system to saturated-absorption spectroscopy of a rovibrational transition of carbonyl sulfide.

Temperature and Velocity Diagnostics of the Red Rectangle from UV Spectra of CO and Ci

The UV spectrum of the Red Rectangle and its central source, HD 44179, was examined using the Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST). Spectra have been obtained of the 0-0, 0-1, and 0-2 vibronic bands of the CO fourth positive system, the 1657 A C I multiplet, and the 1931 A C I line. All of the lines and bands display both absorption and emission components. The components do not display P Cygni profiles, but are nearly symmetrically reversed and show different spreads of radial velocity. The widths and Doppler shifts of each component provide information about the environment of its origin, as do the rotational and vibrational distributions in CO. The 1657 A multiplet is too complex for analysis, but the 1931 A line can be deconvolved into two components: emission with narrow velocity dispersion, 25 km s-1, and absorption with a broad velocity dispersion, 230 km s-1. The radial velocity of these atomic features is consistent with the velocity of the center of mass of this known spectroscopic binary. For the CO bands, we obtained a best fit from a four-component model, consistent for all three bands. There are three emission components and one absorption component. Two emission components display narrow velocity spreads (29 km s-1), and one shows a rotational temperature of 50 K, the other, of about 3000 K. The third emission component has a very wide velocity spread (600 km s-1) and a rotational temperature of about 100 K. The absorption component shows a wide velocity spread (230 km s-1) and a rotational temperature of about 100 K. The high-temperature emission displayed partially-resolved rotational line structure corresponding to levels of J = 50. The Doppler shifts of these features place the narrow, cold emission with one of the binary components and the narrow, hot emission with the center of mass. We discuss these observations with respect to the accretion disk model of this object. We also compare our UV CO observations with the work of others on the IR CO overtone spectra in young stellar objects.

Carbon Isotope Ratios from the First Overtone CO Bands in Metal-Poor Giants.

Carbon Isotope Ratios from the First Overtone CO Bands in Metal-Poor Giants.