714 research outputs found
A near infrared line list for \NH: Analysis of a Kitt Peak spectrum after 35 years
A Fourier Transform (FT) absorption spectrum of room temperature NH3 in the
region 7400 - 8600 cm-1 is analysed using a variational line list and ground
state energies determined using the MARVEL procedure. The spectrum was measured
by Dr Catherine de Bergh in 1980 and is available from the Kitt Peak data
center. The centers and intensities of 8468 ammonia lines were retrieved using
a multiline fitting procedure. 2474 lines are assigned to 21 bands providing
1692 experimental energies in the range 7000 - 9000 cm-1. The spectrum was
assigned by the joint use of the BYTe variational line list and combination
differences. The assignments and experimental energies presented in this work
are the first for ammonia in the region 7400 - 8600 cm-1, considerably
extending the range of known vibrational-excited statesComment: 27 pages, 6 table, 5 figures. Accepted for publication in Journal of
Molecular Spectroscop
First observation of electric-quadrupole infrared transitions in water vapour
Molecular absorption of infrared radiation is generally due to ro-vibrational
electric-dipole transitions. Electric-quadrupole transitions may still occur,
but they are typically a million times weaker than electric-dipole transitions,
rendering their observation extremely challenging. In polyatomic or polar
diatomic molecules, ro-vibrational quadrupole transitions have never been
observed. Here, we report the first direct detection of quadrupole transitions
in water vapor. The detected quadrupole lines have intensity largely above the
standard dipole intensity cut-off of spectroscopic databases and thus are
important for accurate atmospheric and astronomical remote sensing
High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm-1: Part III-Analysis and theoretical modeling of the 12C17O2, 16O12C17O, 17O12C18O, 16O13C17O and 17O13C18O spectra
More than 19,700 transitions belonging to 11 isotopologues of carbon dioxide
have been assigned in the room temperature absorption spectrum of highly 18O
enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down
spectroscopy between 5851 and 6990 cm-1 (1.71-1.43 \mum). This third and last
report is devoted to the analysis of the bands of five 17O containing
isotopologues present at very low concentration in the studied spectra:
16O12C17O, 17O12C18O, 16O13C17O, 17O13C18O and 12C17O2 (627, 728, 637, 738 and
727 in short hand notation). On the basis of the predictions of effective
Hamiltonian models, a total of 1759, 1786, 335, 273 and 551 transitions
belonging to 24, 24, 5, 4 and 7 bands were rovibrationally assigned for 627,
728, 637, 738 and 727, respectively. For comparison, only five bands were
previously measured in the region for the 728 species. All the identified bands
belong to the \deltaP=8 and 9 series of transitions, where P=2V1+V2+3V3 is the
polyad number (Vi are vibrational quantum numbers). The band-by-band analysis
has allowed deriving accurate spectroscopic parameters of 61 bands from a fit
of the measured line positions. Two interpolyad resonance perturbations were
identified
ACCURATE LASER MEASUREMENTS OF THE WATER VAPOR SELF-CONTINUUM ABSORPTION IN FOUR NEAR INFRARED ATMOSPHERIC WINDOWS. A TEST OF THE MT_CKD MODEL.
The semi empirical MT_CKD model of the absorption continuum of water vapor is widely used in atmospheric radiative transfer codes of the atmosphere of Earth and exoplanets but lacks of experimental validation in the atmospheric windows. Recent laboratory measurements by Fourier transform Spectroscopy have led to self-continuum cross-sections much larger than the MT_CKD values in the near infrared transparency windows. _x000d_
In the present work, we report on accurate water vapor absorption continuum measurements by Cavity Ring Down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Laser Spectroscopy (OF-CEAS) at selected spectral points of the transparency windows centered around 4.0, 2.1 and 1.25 m. The temperature dependence of the absorption continuum at 4.38 m and 3.32 m is measured in the 23-39 C range. The self-continuum water vapor absorption is derived either from the baseline variation of spectra recorded for a series of pressure values over a small spectral interval or from baseline monitoring at fixed laser frequency, during pressure ramps. In order to avoid possible bias approaching the water saturation pressure, the maximum pressure value was limited to about 16 Torr, corresponding to a 75% humidity rate._x000d_
After subtraction of the local water monomer lines contribution, self-continuum cross-sections, C, were determined with a few % accuracy from the pressure squared dependence of the spectra base line level. _x000d_
Together with our previous CRDS and OF-CEAS measurements in the 2.1 and 1.6 m windows, the derived water vapor self-continuum provides a unique set of water vapor self-continuum cross-sections for a test of the MT_CKD model in four transparency windows. Although showing some important deviations of the absolute values (up to a factor of 4 at the center of the 2.1 m window), our accurate measurements validate the overall frequency dependence of the MT_CKD2.8 model. _x000d
COMB-ASSISTED CAVITY RING DOWN SPECTROSCOPY OF 17O ENRICHED WATER BETWEEN 7443 AND 7921 CM−1
The room temperature absorption spectrum of water vapour highly enriched in chem{^{17}O} has been recorded by Cavity Ring Down Spectroscopy (CRDS) between 7443 and 7921 wn. Three series of recordings were performed with pressure values around 0.1, 1 and 10 Torr. The frequency calibration of the present spectra benefited of the combination of the CRDS spectrometer to a self-referenced frequency comb. The resulting CRD spectrometer combines excellent frequency accuracy over a broad spectral region with a high sensitivity (Noise Equivalent Absorption, wn). _x000d_
The investigated spectral region corresponds to the high energy range of the first hexade. The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Partridge and Schwenke. Overall about 4150 lines were measured and assigned to 4670 transitions of six water isotopologues (chem{H_2^{16}O}, chem{H_2^{17}O}, chem{H_2^{18}O}, chem{HD^{16}O}, chem{HD^{17}O} and chem{HD^{18}O}). Their intensities span six orders of magnitude from 10 to 10 cm/molecule. Most of the new results concern the chem{H_2^{17}O} and chem{HD^{17}O} isotopologues for which about 1600 and 400 transitions were assigned leading to the determination of 329 and 207 new energy levels, respectively. For comparison only about 300 and four transitions of chem{H_2^{17}O} and chem{HD^{17}O} were previously known in the region, respectively._x000d_
By comparison to highly accurate chem{H_2^{16}O} line positions available in the literature, the average accuracy on our line centers is checked to be on the order of 3 MHz (10 wn) or better for unblended lines. This small uncertainty represents a significant improvement of the line center determination of many chem{H_2^{16}O} lines in the considered region
AN EMPIRICAL SPECTROSCOPIC DATABASE FOR ACETYLENE IN THE REGIONS OF 5850-9415 CM−1
Six studies have been recently devoted to a systematic analysis of the high-resolution near infrared absorption spectrum of acetylene recorded by Cavity Ring Down spectroscopy (CRDS) in Grenoble and by Fourier-transform spectroscopy (FTS) in Brussels and Hefei. On the basis of these works, in the present contribution, we construct an empirical database for acetylene in the 5850 - 9415 region excluding the 6341-7000 interval corresponding to the very strong nub{1}+ nub{3} manifold. The database gathers and extends information included in our CRDS and FTS studies. In particular, the intensities of about 1700 lines measured by CRDS in the 7244-7920 are reported for the first time together with those of several bands of CCH present in natural isotopic abundance in the acetylene sample. _x000d_
The Herman-Wallis coefficients of most of the bands are derived from a fit of the measured intensity values. A recommended line list is provided with positions calculated using empirical spectroscopic parameters of the lower and upper energy vibrational levels and intensities calculated using the derived Herman-Wallis coefficients. This approach allows completing the experimental list by adding missing lines and improving poorly determined positions and intensities. As a result the constructed line list includes a total of 10973 lines belonging to 146 bands of CH and 29 bands of CCH. For comparison the HITRAN2012 database in the same region includes 869 lines of 14 bands, all belonging to CH. Our weakest lines have an intensity on the order of 10 cm/molecule,about three orders of magnitude smaller than the HITRAN intensity cut off. Line profile parameters are added to the line list which is provided in HITRAN format._x000d_
The comparison to the HITRAN2012 line list or to results obtained using the global effective operator approach is discussed in terms of completeness and accuracy._x000d
Stark deceleration of lithium hydride molecules
We describe the production of cold, slow-moving LiH molecules. The molecules
are produced in the ground state using laser ablation and supersonic expansion,
and 68% of the population is transferred to the rotationally excited state
using narrowband radiation at the rotational frequency of 444GHz. The molecules
are then decelerated from 420m/s to 53m/s using a 100 stage Stark decelerator.
We demonstrate and compare two different deceleration modes, one where every
stage is used for deceleration, and another where every third stage decelerates
and the intervening stages are used to focus the molecules more effectively. We
compare our experimental data to the results of simulations and find good
agreement. These simulations include the velocity dependence of the detection
efficiency and the probability of transitions between the weak-field seeking
and strong-field seeking quantum states. Together, the experimental and
simulated data provide information about the spatial extent of the source of
molecules. We consider the prospects for future trapping and sympathetic
cooling experiments.Comment: 14 pages, 6 figures; minor revisions following referee suggestion
Electric quadrupole transitions in carbon dioxide
Recent advances in the high sensitivity spectroscopy have made it possible,
in combination with accurate theoretical predictions, to observe for the first
time very weak electric quadrupole transitions in a polar polyatomic molecule
of water. Here we present accurate theoretical predictions of the complete
quadrupole ro-vibrational spectrum of a non-polar molecule CO, important in
atmospheric and astrophysical applications. Our predictions are validated by
recent cavity enhanced absorption spectroscopy measurements and are used to
assign few weak features in the recent ExoMars ACS MIR spectroscopic
observations of the martian atmosphere. Predicted quadrupole transitions appear
in some of the mid-infrared CO and water vapor transparency regions, making
them important for detection and characterization of the minor absorbers in
water- and CO-rich environments, such as present in the atmospheres of
Earth, Venus and Mars
Electric-quadrupole and magnetic-dipole contributions to the ν₂+ν₃ band of carbon dioxide near 3.3 µm
The recent detections of electric-quadrupole (E2) transitions in water vapor and magnetic-dipole (M1) transitions in carbon dioxide have opened a new field in molecular spectroscopy. While in their present status, the spectroscopic databases provide only electric-dipole (E1) transitions for polyatomic molecules (H_{2}O, CO_{2}, N_{2}O, CH_{4}, O_{3}…), the possible impact of weak E2 and M1 bands to the modeling of the Earth and planetary atmospheres has to be addressed. This is especially important in the case of carbon dioxide for which E2 and M1 bands may be located in spectral windows of weak E1 absorption. In the present work, a high sensitivity absorption spectrum of CO_{2} is recorded by Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OFCEAS) in the 3.3 µm transparency window of carbon dioxide. The studied spectral interval corresponds to the region where M1 transitions of the ν_{2}+ν_{3} band of carbon dioxide were recently identified in the spectrum of the Martian atmosphere. Here, both M1 and E2 transitions of the ν_{2}+ν_{3} band are detected by OFCEAS. Using recent ab initio calculations of the E2 spectrum of {12}^C^{16}O_{2}, intensity measurements of five M1 lines and three E2 lines allow us to disentangle the M1 and E2 contributions. Indeed, E2 intensity values (on the order of a few 10^{–29} cm/molecule) are found in reasonable agreement with ab initio calculations while the intensity of the M1 lines (including an E2 contribution) agree very well with recent very long path measurements by Fourier Transform spectroscopy. We thus conclude that both E2 and M1 transitions should be systematically incorporated in the CO_{2} line list provided by spectroscopic databases
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