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Spectra of water-CO2 dimers are studied using a tunable mid-infrared source to probe a pulsed slit jet supersonic expansion. H2O-CO2 and D2O-CO2 are observed in the CO2 nu3 fundamental region (~2350 cm-1), D2O-CO2 is also observed in the D2O nu3 fundamental region (~2790 cm-1), and HDO-CO2 is observed in the HDO O-D stretch fundamental region (~2720 cm-1), all for the first time in these regions. Analysis of the spectra yields excited state rotational parameters and vibrational shifts. They also yield the first experimental values of the ground state internal rotation tunneling splittings for D2O-CO2 (0.003 cm-1) and HDO-CO2 (0.0234 cm-1). The latter value is a direct determination made possible by the reduced symmetry of HDO-CO2. These results provide stringent and easily interpreted tests for theoretical water - CO2 potential energy surface calculations., Comment: 19 pages, 6 figure and 5 tables

The infrared spectrum of the weakly-bound C2H4-CO2 complex is investigated in the region of the nu3 fundamental band of CO2 (~2350 cm-1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. The spacing of the various K-subbands in this perpendicular spectrum is very irregular, and the pattern of irregularity is quite different from that observed previously in another C2H4-CO2 band by Bemish et al. [J. Chem. Phys. 103, 7788 (1995)]. But by allowing for the different symmetry of the nu3 (CO2) upper vibrational state, both results can be strikingly well explained using the 'double internal rotor' model as described by Bemish et al., 27 page and 6 figures

The infrared spectrum of the weakly-bound CO2-Ne complex is studied in the region of the carbon dioxide nu3 fundamental vibration (~2350 cm-1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. For the fundamental CO2 transition (v1, v2l2, v3) = (0001), Comment: 4 figures, 2 tables, 35 pages

This paper describes the 2020 release of the GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), developed and maintained at LMD since 1974. GEISA is the reference database for several current or planned Thermal and Short-Wave InfraRed (TIR and SWIR) space missions IASI (Infrared Atmospheric Sounding Interferometer), IASI-NG (IASI New Generation), MicroCarb (Carbon Dioxide Monitoring Mission), Merlin (MEthane Remote sensing LIdar missioN). It is actually a compilation of three databases: the “line parameters database”, the “cross-section sub-database” and the “microphysical and optical properties of atmospheric aerosols sub-database”. The new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data. The GEISA-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10−6 to 35877 cm−1. In this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (HONO, COFCl, CH3F, CH3I, RuO4, H2C3H2 (isomer of C3H4)) corresponding to 15 isotopic species. The compilation can be accessed through the AERIS data and services center for the atmosphere website (https://geisa.aeris-data.fr/), with the development of a powerful graphical tool and convenient searching, filtering, and plotting of data using modern technologies (PostgreSQL database, REST API, VueJS, Plotly). Based on four examples (H2O, O3, O2 and SF6), this paper also shows how the LMD in house validation algorithm SPARTE (Spectroscopic Parameters And Radiative Transfer Evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into GEISA and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer).

The rovibrational band corresponding to a double excitation of the OH symmetric stretch of the H2O unit in the H2O-CO2 van der Waals complex has been recorded using CW-CRDS and a pulsed slit expansion seeded in He. The set-up is presented. The rotational analysis of this band is detailed and the results of the global fit of these data with those of the other 2OH excitation band and of the ground vibrational states are reported including data from the literature. The tunneling frequency and the vibrational predissociation lifetime are shown to decrease with vibrational excitation.

Infrared spectra of Rg1,2 - C6H6 complexes (Rg = He, Ne, Ar) are observed in the region of the nu12 fundamental of C6H6 using a pulsed supersonic jet expansion and a tunable optical parametric oscillator laser source. The mixed trimer He - Ne - C6H6 is also detected. Four bands are analyzed for each complex, namely nu12 itself (~3048 cm-1) and three linked combination bands (~3079, 3100, and 3102 cm-1). The results are consistent with previous ultraviolet and microwave results, with Ne2 - C6H6 and He - Ne - C6H6 being analyzed spectroscopically here for the first time., 22 pages, 3 figures

We extend studies of micro-solvation of carbon monoxide by a combination of high-resolution IR spectroscopy and ab initio calculations. Spectra of the (H2O)4-CO and (D2O)4-CO pentamers are observed in the C-O stretch fundamental region (~2150 cm-1). The H2O containing spectrum is broadened by predissociation, but that of D2O is sharp, enabling detailed analysis which gives a precise band origin and rotational parameters. Ab initio calculations are employed to confirm the assignment to (water)4-CO and to determine the structure, in which the geometry of the (water)4 fragment is a cyclic ring very similar to the isolated water tetramer. The CO fragment is located "above" the ring plane, with a partial hydrogen bond between the C atom and one of the "free" protons (deuterons) of the water tetramer. Together with previous results on D2O-CO, (D2O)2-CO, and (D2O)3-CO, this represents a probe of the four initial steps in the solvation of carbon monoxide at high resolution., 27 page, 3 figures

The infrared spectrum of the weakly-bound CO2-Xe complex is studied in the region of the carbon dioxide nu3 fundamental vibration (~2350 cm-1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. The Xe isotope dependence of the spectrum is modeled by scaling the vibrational and rotational parameters, with the help of previous microwave data. The scaling model provides a good simulation of the observed broadening and (partial) splitting of transitions in the fundamental band, and it is essential for understanding the intermolecular bending combination band where some transitions are completely split by isotope effects. The combination band is influenced by a significant bend-stretch Coriolis interaction and by the relatively large Xe isotope dependence of the intermolecular stretch frequency. The weak CO2-Xe spectrum corresponding to the (0111), Comment: 55 pages, 5 figures and 4 tables

The O–D stretch rovibrational spectra of N2–D2O and N2–DOH were measured and analyzed. A combination band involving the in-plane N2 bending vibration was also observed. These bands were recorded using a pulsed-slit supersonic jet expansion and a mid-infrared tunable optical parametric oscillator. The spectra were analyzed by considering the feasible tunneling motions, and transitions were fitted to independent asymmetric rotors for each tunneling state. The rotational constants of the four tunneling components of N2–D2O were retrieved for the excited vibrational states. A two order of magnitude increase in the tunneling splittings is observed for the asymmetric O–D stretch (ν3 in D2O) excitation compared to the symmetric stretch (ν1 in D2O) and to the ground vibrational state. This last finding indicates that the ν3 vibrational state is likely perturbed by a combination state that includes ν1. Finally, the observation of a local perturbation in the ν3 vibrational band, affecting the positions of few rovibrational levels, provides an experimental lower limit of the dissociation energy of the complex, D0 > 120 cm−1.

The weak infrared spectrum of CO2-Ar corresponding to the (0111), Comment: 19 pages, 1 table, and 3 figures

Infrared spectra of the CO2-N2 dimer are observed in the carbon dioxide nu3 asymmetric stretch region (~2350 cm-1) using a tunable infrared optical parametric oscillator to probe a pulsed slit jet supersonic expansion. Previous results for the b-type fundamental band are extended to higher values of Ka. An a-type combination band involving the lowest in-plane intermolecular bending mode is observed. This yields a value of 21.4 cm-1, and represents the first experimental determination of an intermolecular mode for CO2-N2. This intermolecular frequency is at odds with the value of 45.9 cm-1 obtained from a recent 4D intermolecular potential energy surface. In addition, two weak bands near 2337 cm-1 are assigned to the CO2 hot band transition (v1, v2, l2, v3) = (0111), Comment: 16 pages, 3 figures

Rotationally-resolved infrared spectra of N2O–Ar and N2O–Kr are studied in the region of the N2O ν1 vibration (≈ 2224 cm-1) using a tunable Quantum Cascade laser source to probe a pulsed supersonic jet. The N2O–Kr ν1 fundamental band is re-analyzed, together with previous ν3 band data, using a unified scheme to fit the (small) observed Kr isotope splittings. This scheme is then transferred to analyze the bending combination band of N2O–Kr near 2257 cm-1 where isotope effects are much larger due to stretch-bend interactions. As a result, N2O–Kr intermolecular bend (33.29 cm-1) and stretch (34.48 cm-1) frequencies are directly determined for the first time. Weak spectra are detected for both N2O–Ar and –Kr corresponding to the (ν1, ν2l2, ν3) = (1110) ← (0110) hot band of N2O. Their analysis yields the magnitude of the splitting of the N2O ν2 bending mode into in-plane and out-of-plane components. These splittings are found to be significantly smaller than those observed in the analogous CO2-containing dimers.

Spectra of ethylene dimers and trimers are studied in the nu11 and (for the dimer) nu9 fundamental band regions of C2H4 (~2990 and 3100 cm-1) using a tunable optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. The deuterated trimer has been observed previously, but this represents the first rotationally resolved spectrum of (C2H4)3. The results support the previously determined cross-shaped (D2d) dimer and barrel-shaped (C3h or C3) trimer structures. However, the dimer spectrum in the nu9 fundamental region of C2H4 is apparently very perturbed and a previous rotational analysis is not well verified., 21 pages, 4 figures

Extensive infrared spectra of the weakly-bound CO2-CO dimer are observed in the carbon dioxide ν3 asymmetric stretch region (≈2350 cm−1) using a tunable infrared OPO laser source to probe a pulsed ...

Three combination bands involving intermolecular modes of the most stable isomer of the OC–N2O van der Waals complex have been observed, two in the carbon monoxide CO stretch region (∼2150 cm–1) and one in the ν3 asymmetric stretch region of N2O (∼2223 cm–1). Vibrational assignment is achieved by comparison with data recently published (Barclay, A.; et al. Chem. Phys. Lett. 2016, 62, 651), concerning OC–CO2. Two of these bands involve the same intermolecular mode, one with the CO stretch and the other with the ν3 asymmetric stretch of N2O. The values of intermolecular frequency deduced from these two bands agree very well, showing no significant dependence on intramolecular vibrational excitation.

Infrared spectra in the carbon monoxide CO stretch region (∼2150 cm-1) and in the ν3 asymmetric stretch region of N2O (∼2223 cm-1) are assigned to the previously unobserved O-bonded form of the CO-N2O dimer ("isomer 2"). This van der Waals complex has a planar skewed T-shaped structure like that of the previously observed C-bonded form ("isomer 1"), but with the CO rotated by 180°. The effective intermolecular distance between the centers of mass is 3.51 A for isomer 2 as compared to 3.88 A for isomer 1. In addition to the fundamental band, two combination bands are observed for isomer 2, yielding values for two intermolecular vibrational modes: 14.502(5) cm-1 for the coupled disrotatory motion or the uncoupled CO rock and 21.219(5) cm-1 for the out-of-plane rock. We show that the published ab initio study on this system is inadequate in predicting the intermolecular frequencies for isomer 2 of CO-N2O.

The infrared spectrum of the cross-shaped van der Waals complex CO2–CS2 is observed in the region of the CO2 ν3 fundamental band (≈2350 cm−1) using a tuneable diode laser to probe a pulsed supersonic slit jet expansion. Two combination bands are assigned, corresponding to the intermolecular torsion and CO2 bend modes, and their positions and rotational structure agree extremely well (

The weakly-bound molecular clusters (D2O)2-CO and (D2O)3-CO are observed in the C-O stretch fundamental region (~2150 cm-1), and their rotationally-resolved infrared spectra yield precise rotational parameters. The corresponding H2O clusters are also observed, but their bands are broadened by predissociation, preventing detailed analysis. The rotational parameters are insufficient in themselves to determine cluster structures, so ab initio calculations are employed, and good agreement between the experimental and theory is found for the most stable cluster isomers, yielding the basic cluster geometries as well as confirming the assignments to (D2O)2-CO and (D2O)3-CO. The trimer, (D2O)2-CO, has a near-planar geometry with one D atom from each D2O slightly out of the plane. The tetramer, (D2O)3-CO, has the water molecules arranged in a cyclic quasi-planar ring similar to the water trimer, with the carbon monoxide located 'above' the ring and roughly parallel to its plane. The tunneling effects observed in the free water dimer and trimer are quenched by the presence of CO. The previously observed water-CO dimer together with the trimer and tetramer reported here represent the first three steps in the solvation of carbon monoxide., 3 figures and 25 pages

The jet-cooled spectrum (Trot = 12K) of the H2O–CO2 van der Waals complex has been recorded in the 1.4 μm region by cavity ring-down spectroscopy. Two b-type vibrational bands have been observed and analysed. The rotational assignment has been achieved using a different asymmetric rotor Hamiltonian for each nuclear spin species, accounting for the internal rotation of the H2O and CO2 units. The band at 7247 cm-1 is assigned to (101) in terms of the (v1v2v3) vibrational quantum number of the H2O monomer. The band at 7238 cm-1 is assigned to (200) + an intermolecular mode (v12) excited in the complex. Vibration-rotation constants are provided for the excited states. The symmetry of the wavefunction, the effect of vibrational excitation on the tunnelling dynamics and the vibrational assignment are discussed., SCOPUS: ar.j, info:eu-repo/semantics/published

Rovibrational energy level calculations using a high-level intermolecular potential surface are reported for H2O-CO and D2O-CO. They predict the ground K = 1 levels to lie about 20 (12) cm-1 above K = 0 for H2O-CO (D2O-CO) in good agreement with past experiment. But the first excited K = 1 levels are predicted to lie about 3 cm-1 below their K = 0 counterparts in both cases. Intensity calculations also indicate that mid-infrared transitions from the K = 0 ground state to this seemingly anomalous excited K = 1 state should be observable. These predictions are strikingly verified by new spectroscopic measurements covering the C-O stretch region around 2200 cm-1 for H2O-CO, D2O-CO, and HOD-CO, and the O-D stretch region around 2700 cm-1 for D2O-CO, HOD-CO, and DOH-CO. The experiments probe a pulsed supersonic slit jet expansion using tunable infrared quantum cascade laser or optical parametric oscillator sources. Discrete perturbations in the O-D stretch region give an experimental lower limit of about 340 cm-1 for D2O-CO, as compared to our calculated binding energy of 368 cm-1. Wavefunction plots are presented to help understand the intermolecular dynamics of H2O-CO. Coriolis interactions are invoked to explain the seemingly anomalous energies of the first excited K = 1 levels., Comment: 46 pages, 8 figures, and 9 tables

The fundamental O-D stretch region (2600 - 2800 cm-1) of the fully deuterated water dimer, (D2O)2, is studied using a pulsed supersonic slit jet source and a tunable optical parametric oscillator source. Relatively high spectral resolution (0.002 cm-1) enables all six dimer tunneling components to be observed, in most cases, for the acceptor asymmetric O-D stretch, the donor free O-D stretch, and the donor bound O-D stretch vibrations. The dominant acceptor switching tunneling splittings are observed to decrease moderately in the excited O-D stretch states, to roughly 75% of their ground state values, whereas the smaller donor-acceptor interchange splittings show more dramatic and irregular decreases. Excited state predissociation lifetimes, as determined from observed line broadening, show large variations (0.2 to 5 nanoseconds) depending on vibrational state, K-value, and tunneling symmetry. Another very weak band is tentatively assigned to a combination mode involving an intramolecular O-D stretch plus an intermolecular twist overtone. Asymmetric O-D stretch bands of the mixed isotopologue dimers D2O-DOH and D2O-HOD are also observed and analyzed., 35 pages, 5 tables and 8 figures

The infrared spectrum of the cross-shaped van der Waals complex N2O-CS2 is observed in the region of the N2O nu1 fundamental band (~2220 cm-1) using a tuneable diode laser to probe a pulsed supersonic slit jet expansion. Both 14N- and 15N-substituted species are studied. Analysis of their spectra establishes that this dimer has a cross-shaped structure, similar to its isoelectronic cousin CO2-CS2. This is the first spectroscopic observation of N2O-CS2, and the molecular parameters determined here should be useful for detection of its pure rotational microwave spectrum., 10 Pages, 3 figures

We report the infrared spectrum of H$_2$C$_4$-(OCS)$_2$ trimer in the region of the nu1 fundamental vibration of the OCS monomer. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser. Both H$_2$C$_4$-(OCS)$_2$ and D$_2$C$_4$-(OCS)$_2$ are studied. Analysis of their spectra establishes that the trimer has C$_2$ point group symmetry. Theoretical calculations performed to find stationary points on the potential energy surface confirm that the observed structure is the most stable form. The experimental rotational parameters are in very good agreement with those computed using double hybrid functionals., Comment: 23 pages, 3 figures

Infrared spectra of Ar–C2D2 are observed in the region of the ν3 fundamental band (asymmetric C–D stretch, ≈2440 cm−1) using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion from a cooled nozzle. Transitions are assigned involving K = 0–2 in the ground vibrational state, and K = 0–4 in the excited state. The intermolecular bending combination band is also observed, giving a bending frequency of 4.798 cm−1. Despite this low bending frequency, the Ar–C2D2 spectrum qualitatively resembles that of a normal semi-rigid molecule, in contrast to He– and Ne–C2D2 which are much closer to the limit of free internal rotation.

High quality line parameters of the band systems of ethane are required for accurate characterization of spectral features observed in the atmospheres of Jovian planets and their satellites. To date, experimental characterization of the excited vibrational states lying below 1300 cm −1 has been made. This includes the torsional bands around 35 µm, ν 9 (820 cm −1 ), ν 3 (990 cm −1 ), ν 12 − ν 9 (380 cm −1 ) and ν 9 + ν 4 − ν 4 (830 cm −1 ) bands. These earlier high resolution ro-vibrational analyses were made to experimental accuracy. Here, we report a detailed analysis of the weak ν 6 band in the 1340–1410 cm −1 region using a spectrum recorded at a resolution of 0.003 cm −1 and temperature of 200 K. The Hamiltonian model included couplings between ν 6 and ν 9 (in particular with ν 9 +2 ν 4 with which it is resonantly coupled) as well as couplings between ν 6 and ν 8 . An excellent fit to within experimental accuracy was obtained. Taking the results of this 5-state fit, together with earlier results on lower lying vibrations, we now have experimental characterization for torsion–vibration states of ethane lying below 1400 cm −1 .

Infrared spectra of the CO2 CO dimer are observed in the carbon monoxide CO stretch region (≈2150 cm−1). Combination bands yield the first experimental determinations of intermolecular mode frequencies for the planar T-shaped C-bonded form (‘isomer 1’): 24.34 cm−1 for the in-plane CO rock and 43.96 cm−1 for the out-of-plane CO rock. These values are significantly higher than the analogous modes of the O-bonded form (‘isomer 2’), previously determined to be 14.19 and 22.68 cm−1, respectively. New results are also reported for both isomers of the 12C18O2-substituted form of the dimer. Weak ‘satellite bands’ observed for both isomers are tentatively assigned to the trimer He CO2 CO.

Spectra of dimers and trimers containing C6D6 and He, Ne, Ar, or H2 are observed in the region of the C6D6 ν12 fundamental using a pulsed supersonic jet expansion and a tunable optical parametric oscillator laser source. These are the first reported infrared spectra of hydrogen – benzene complexes. Two bands coupled by anharmonic resonance are studied for each complex: the ν12 fundamental itself (≈2289 cm−1) and the ν2 + ν13 combination band (≈2276 cm−1). Vibrational shifts for the trimers are found to be approximately twice those of the corresponding dimer. Effective intermolecular separations for (H2)1,2-C6D6 are about 3.46 A, similar to those determined previously from electronic spectra of (H2)1,2-C6H6 and also similar to (Ne)1,2-C6D6.

Only a few weakly-bound complexes containing the O2 molecule have been characterized by high resolution spectroscopy, no doubt due to the complications added by the oxygen molecule's unpaired electron spin. Here we report an extensive infrared spectrum of CO-O2, observed in the CO fundamental band region using a tunable quantum cascade laser to probe a pulsed supersonic jet expansion. The rotational energy level pattern derived from the spectrum consists of stacks of levels characterized by the total angular momentum, J, and its projection on the intermolecular axis, K. Five such stacks are observed in the ground vibrational state, and ten in the excited state (v(CO) = 1). They are divided into two groups, with no observed transitions between groups. The groups correspond to different projections of the O2 electron spin, and correlate with the two lowest rotational states of O2, (N, J) = (1, 0) and (1, 2). The rotational constant of the lowest K = 0 stack implies an effective intermolecular separation of 3.82 Angstroms, but this should be interpreted with caution since it ignores possible effects of electron spin. A new high-level 4-dimensional potential energy surface is developed for CO-O2, and rotational energy levels are calculated for this surface, ignoring electron spin. By comparing calculated and observed levels, it is possible to assign detailed quantum labels to the observed level stacks., 35 pages and 8 figures

The infrared spectra of the weakly-bound dimers OCS-HCCCCH, in the region of the nu1 fundamental band of OCS (2050 cm-1), and N2O-HCCCCH, in the region of the nu1 fundamental band of N2O (2200 cm-1), were observed in a pulsed supersonic slit jet expansion probed with tunable diode/QCL lasers. Both OCS-HCCCCH and N2O-HCCCCH were found to have planar structure with side-by-side monomer units having nearly parallel axes. These bands have hybrid rotational structure which allows for estimates of the orientation of OCS and N2O in the plane of their respective dimers. Analogous bands for OCS-DCCCCD and N2O-DCCCCD were also observed and found to be consistent with the normal isotopologues. Various levels of ab initio calculations were performed to find stationary points on the potential energy surface, optimized structures and interaction energies. Four stable geometries were found for OCS-HCCCCH and three for N2O-HCCCCH. The rotational parameters at CCSD(T*)-F12c level of theory give results in very good agreement with those obtained from the observed spectra. In both dimers, the experimental structure corresponds to the lowest energy isomer., 55 pages and four figures

Ethane is the second most abundant hydrocarbon detected in the outer planets. Although the torsional mode is not infrared active in the lowest order, the strongest feature in this band can be seen near 289 cm −1 in the CASSINI CIRS spectrum of Titan. Prior laboratory studies have characterized the torsional frequencies to high accuracy and measured the intensities to temperatures as low as 208 K. However, for the interpretation of the far-infrared observations of Titan, further investigation was needed to determine the intensities at lower temperatures and to higher accuracy. The spectrum of C 2 H 6 was investigated from 220 to 330 cm −1 to obtain the band strengths of the torsional fundamental ν 4 (near 289 cm −1 ) and the first torsional hot band ( 2 ν 4 − ν 4 ). Seven laboratory spectra were obtained at resolutions of 0.01 and 0.02 cm −1 using a Bruker IFS-125 Fourier transform spectrometer at the Jet Propulsion Laboratory. The interferometer was coupled to a coolable multi-pass absorption cell set to an optical path length of 52 m. The range of temperatures was 166–292 K with the lower temperatures being most relevant to the stratosphere of Titan. The ethane sample pressures ranged from 35 to 254 Torr. The modeling of the transition intensities required the expansion of the dipole moment operator to higher order; this introduced Herman-Wallis like terms. The fitting process involved five independent dipole constants and a single self-broadening parameter. The results presented should lead to an improved understanding of the methane cycle in planetary atmospheres and permit other molecular features in the CIRS spectra to be identified.

Three new infrared bands of the weakly-bound He-OCS complex are studied, using tunable lasers to probe a pulsed supersonic slit jet expansion. They correspond to the (0400), Comment: 16 pages, 1 figure, 4 tables