Weak Hot Bands Research Articles

Spectra of CO2‐Kr in the 4.3 μm region: Intermolecular Bend and Symmetry Breaking of the Intramolecular CO2 Bend

AbstractThe infrared spectrum of CO2‐Kr complex is studied in the region of the carbon dioxide ν3 fundamental vibration (≈2350 cm−1). Tunable IR radiation from an OPO is employed to record absorption spectrum of the complex generated in a pulsed supersonic slit jet. The spectrum exhibits broadening and splitting of transitions due to mass dependence of the five Kr isotopes with natural abundances exceeding 2 %. Good simulation of the spectrum is achieved by scaling the vibrational and rotational parameters. This scaling model is particularly important for the combination band involving the intermolecular bending mode where many isotope splittings are observed. As with other CO2‐rare gas complexes, we also observe weak hot bands of CO2‐Kr transitions corresponding to the hot band originating in the CO2 intramolecular bend. From these we determine a splitting of 1.418 cm−1 between the in‐plane and out‐of‐plane bend of CO2, due to the neighboring Kr atom.

Photoswitchable Photon Upconversion from Turn-on Mode Fluorescent Diarylethenes

Photon upconversion (UC) is one kind of anti-Stokes shift process, which generally requires a combination of two or more low-energy photons to produce one high-energy photon. However, another inter...

Temperature-dependent line parameter study of acetylene transitions near 3 µm

Knowledge of the acetylene spectrum is important for astrophysics, atmospheric, and combustion chemistry research. Twelve acetylene transitions across eleven bands have been studied between 3335.0 and 3336.5 cm−1 with a tunable interband cascade laser. Linestrengths and temperature-dependent lineshape parameters, including collisional broadening and narrowing, are reported through Voigt, Rautian, and Galatry lineshape fits to two strong cold band transitions. Measurements were made in pure acetylene, as well as with diluents argon, nitrogen, and methane, over a temperature range of 296–637 K and pressures of 5–90 Torr. Linestrengths and temperature-dependent self-broadening coefficients are also reported for ten weak hot band transitions through Voigt lineshape fits, measured between 296–513 K and 5–20 Torr. Line parameter measurements are found to be in good agreement with the literature and extend experimental lineshape studies of acetylene into new rovibrational bands, a sparsely-studied temperature regime, and a new perturber: methane.

Cavity ring-down spectroscopy measurements of l-type doubling of hot bands in Δ vibrational states of OCS near 5.2 μm

We investigated the l-type doubling in the (1420) ← (0220) weak hot band transition of carbonyl sulphide (OCS) for l = 2 (i.e. Δ state) vibrational state. High-resolution spectroscopic measurements of l-doublet splittings of OCS were carried out using cavity ring-down spectroscopy (CRDS) technique employing a continuous-wave (cw) external-cavity quantum cascade laser (EC-QCL) operating at ∼5.2 μm. The rotationally resolved spectra of l-doublet splittings between the parity doublet e and f sub-states of OCS were recorded by probing the rotational lines from J = 22 to J = 29 in the R branch belonging to the weak hot band transition. Subsequently, we determined the l-type doubling constant, transition dipole moment, rotational constant and centrifugal distortion constant for both e and f components of the (1420) vibrational state with relatively high rotational states of OCS. As the measurement of l-doublet splitting in l = 2 or higher states of OCS remains challenging due to extremely small splitting, therefore our findings suggest that the observation of the l-type doubling in Δ vibrational state (l = 2) with new values of the several spectroscopic parameters as mentioned above will be useful for better understanding of linear polyatomic molecular properties in general from high-resolution spectroscopic data.

High sensitivity CRDS of CO2 in the 1.74 µm transparency window. A validation test for the spectroscopic databases

The very weak absorption spectrum of natural CO2 near 1.74 µm (5702–5879 cm−1) is studied at high sensitivity. The investigated region corresponds to a transparency window of very weak opacity which is of particular interest for Venus. Very weak lines with intensity value as low as 10−30 cm/molecule at 296 K are detected by Cavity Ring Down Spectroscopy. On the basis of the predictions of effective Hamiltonian models, 1135 lines of six carbon dioxide isotopologues - 12C16O2, 13C16O2, 16O12C18O, 16O12C17O, 16O13C18O and 16O13C17O - were rovibrationnally assigned to 26 bands. The accurate spectroscopic parameters of 16 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are 8 × 10−4 cm−1).These newly observed bands include perturbed bands, weak hot bands and bands of minor isotopologues (in particular 16O12C18O in natural abundance) and provide critical validation tests for the most recent spectroscopic databases. The comparison to the Carbon Dioxide Spectroscopic Databank (CDSD), HITRAN2016 database and recent ab initio line lists is presented. Deficiencies are evidenced for some weak perpendicular bands of the HITRAN2016 list and identified as due to inaccurate CDSD intensities which were preferred to ab initio intensities. While Ames and UCL ab initio intensities are believed to be accurate within a few % for the strong unperturbed bands, the reported measurements allow testing important (>50%) differences between ab initio values of some weak perturbed bands.

Fluorescence Photoswitching of a Diarylethene by Irradiation with Single-Wavelength Visible Light.

Photoswitchable turn-on mode fluorescent molecules have been so far successfully used in super-resolution fluorescence microscopies. Here, we report on fluorescence photoswitching of 1,2-bis(2-ethyl-6-phenyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (1) by irradiation with single-wavelength visible (420 nm < λ < 470 nm) light, the wavelength of which is longer than the 0-0 transition of open-ring isomer 1a, without UV light excitation. By absorbing very weak hot bands or Urbach tails 1a underwent a cyclization reaction to produce fluorescent closed-ring isomer 1b. Both cyclization and cycloreversion reactions of 1 took place with the visible light in the far off-resonance region of the absorption edge. Based on numerical simulations of the formation process of 1b from 1a by irradiation with 450 nm light, weak absorption coefficients at 450 nm in n-hexane and CCl4 were estimated to be 0.084 and 0.19 M-1 cm-1, respectively. The reversible fluorescence photoswitching with the single visible light is advantageously applicable to super-resolution fluorescence imaging in biological systems.

High sensitivity Cavity Ring Down spectroscopy of carbon dioxide in the 1.19–1.26 µm region

A Cavity Ring Down spectrometer using a fiber-connected External Cavity Diode Laser (ECDL) as light source has been developed to access the 1.26–1.19μm region. We present here the first application of this newly developed CW-CRDS spectrometer to the study of the highly sensitive spectrum of natural carbon dioxide between 7909 and 8370cm−1. The spectrum is dominated by the ν1+3ν3 dyad at 8192.55 and 8293.95cm−1 which forms the low energy border of the 1.2µm transparency window of importance for planetary applications. The achieved sensitivity (noise equivalent absorption, αmin, in the 10−10–10−11cm−1 range) allowed detection of numerous new transitions with intensity values down to 10−30cm/molecule, in particular hot bands reaching upper states with energy up to about 10,600cm−1.More than 3400 transitions belonging to the six major isotopologues of ‘natural’ carbon dioxide were assigned using the predictions of effective Hamiltonian (EH) models. A total of 2027, 442, 548, 303, 92 and 13 transitions belonging to 37, 9, 8, 4, 2 and 1 bands were rovibrationnally assigned for 12C16O2, 13C16O2, 16O12C18O, 16O12C17O, 16O13C18O and 16O13C17O, respectively. For comparison, only 14 12C16O2 absorption bands were previously known in the region (mostly from Venus spectra). Intensity values range between 2.1×10−30 and 2.4×10−24cm/molecule. All the identified bands correspond to the ΔP=11 series of transitions, where P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The overall agreement of the EH predicted and measured line positions is very good (for instance, average and rms deviations of 0.64×10−3 and 3.8×10−3cm−1 for 12C16O2, respectively).The band-by-band analysis provided accurate spectroscopic parameters of 57 bands from a fit of the measured line positions. The global fits of the obtained intensity values of the ΔP=11 series of transitions were used to refine the corresponding set of effective dipole moment (EDM) parameters of the six studied isotopologues.The obtained results will help to improve the spectral line parameters of carbon dioxide in the most currently used spectroscopic databases. In particular, the calculated band intensities of a few weak hot bands are now in good agreement with the observations.

Fourier transform spectroscopy using a synchrotron source: Characterization of the instrument line shape and acetylene line parameters around 100 μm

The acetylene 100μm spectral region of astrophysical interest was studied to retrieve absolute line positions and intensities of weak hot bands. An absorption path of 150m was used and the spectra were recorded using the far-infrared AILES beamline of the synchrotron SOLEIL and a Bruker IFS 125-HR. To achieve accurate measurements from FT spectra using the full beam of the synchrotron, special cares have been taken into account concerning the apparatus function and especially the optical weighting. The wavenumber dependence of the size of the synchrotron beam was modeled leading to similar results that have been previously obtained for the analysis of the ν5–ν4 band ([8] Jacquemart et al., J Quant Spectrosc Radiat Transfer 2010;111:1223–33) but with a better precision. In the present work, line positions and intensities have been measured for the first time for 816 transitions of 12C2H2 belonging to 17 bands between 51 and 215cm−1. The accuracy of measurements are estimated to be around 0.1×10−3cm−1 for line positions and between 5 and 10% for intensities depending on the strength of the transitions. The spectroscopic knowledge of these hot bands is of importance especially for theoretical and astrophysical applications.

Rotational analysis of weak (4, 6) hot band in the comet-tail ( A2Π i– X2Σ +) system of the CO +

The ro-vibrational spectrum of the weak (4, 6) hot band in the comet-tail ( A 2Π i – X 2Σ +) system of CO + is observed by employing optical heterodyne and magnetic rotation enhanced velocity modulation spectroscopy. One hundred and twenty-four spectral lines are assigned to this band; thus, precise molecular constants of the levels involved are obtained from a weighted nonlinear least-squares fitting procedure combining with our previous spectrum of the (3, 6) band.

Line mixing and speed dependence in CO 2 at 6227.9 cm −1: Constrained multispectrum analysis of intensities and line shapes in the 30013 ← 00001 band

Line position, intensity and line shape parameters (Lorentz widths, pressure shifts, line mixing, speed dependence) are reported for transitions of the 30013 ← 00001 band of 16O 12C 16O ( ν 0 = 6227.9 cm −1). The results are determined from 26 high-resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath-Pierce Fourier transform spectrometer. To minimize the systematic errors of the retrieved parameters, we constrained the multispectrum nonlinear least squares retrieval technique to use quantum mechanical expressions for the rovibrational energies and intensities rather than retrieving the individual positions and intensities line by line. Self- and air-broadened Lorentz width and pressure-induced shift, speed dependence and line mixing (off-diagonal relaxation matrix elements) coefficients were adjusted individually. Errors were further reduced by simultaneously fitting the interfering absorptions from the weak 30012 ← 00001 band of 16O 13C 16O as well as the weak hot bands 31113 ← 01101, 32213 ← 02201, 40014 ← 10002 and 40013 ← 10001 of 16O 12C 16O in this spectral window. This study complements our previous work on line mixing and speed dependence in the 30012 ← 00001 band ( ν 0 = 6347.8 cm −1) [V.M. Devi, D.C. Benner, L.R. Brown, C.E. Miller, R.A. Toth, J. Mol. Spectrosc. 242 (2007) 90-117] and provides key data needed to improve atmospheric remote sensing of CO 2.

Line mixing and speed dependence in CO 2 at 6348 cm −1: Positions, intensities, and air- and self-broadening derived with constrained multispectrum analysis

Intensity and line shape parameters which predict spectral lines with absolute accuracies better than 0.3% have been determined for transitions of the 30012 ← 00001 band of 16O 12C 16O centered near 6348 cm −1 from 26 high resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath–Pierce Fourier transform spectrometer. To maximize the accuracies of the retrieved parameters, the multispectrum non-linear least squares retrieval technique was modified to adjust the rovibrational constants ( G, B, D, etc.) and intensity parameters, including Herman–Wallis terms, rather than retrieving the individual positions and intensities. Speed-dependent Voigt line shapes with line mixing were required to remove systematic errors in the fit residuals. Self- and air-broadening (widths and pressure-induced shifts, speed dependence parameters) and line mixing (off-diagonal relaxation matrix elements) coefficients were thus obtained in the multispectrum fit. Remaining errors were minimized by fitting the weak 30011 ← 00001 band of 16O 13C 16O as well as the weak hot bands 31112 ← 01101, 32212 ← 02201, 40012 ← 10001, and 40013 ← 10002 of 16O 12C 16O that contribute interfering absorptions in this spectral window. This study presents the most extensive set of measurements to date for self- and air-broadening and self- and air-shift coefficients of a near infrared band of CO 2. This is also the first study where line mixing parameters have been experimentally determined for any parallel CO 2 band.

Measurements of rovibronic line oscillator strengths of N2 in the 83.4 nm region: A high‐resolution high‐temperature study

We report the rovibronic line oscillator strengths of N2 in the 83.4 nm region at high temperatures measured by using ultrahigh‐resolution photoabsorption spectroscopy. The measurements have been carried out using a resolution of 6.5 × 10−4 nm and at temperatures of 600, 535, and 295 K. The N2 absorption features in the 83.4 nm region mainly involve the (0,0) band of the c′6‐X transition and the weaker (2,0) band of the c4‐X and the (25,0) band of the b′–X transitions. Spectral perturbation effects in the c′6‐X transition have been observed at J (rotational quantum number) &gt;14. The presence of weak transitions and hot band transitions further contribute to the spectral complexity, especially in the long wavelength side. By integrating over each individual absorption profile for each rotational line up to J = 16, the rovibronic line oscillator strengths of the (0,0) c′6‐X transition of N2 are measured. For the spectral regions with strong perturbations and overlapping by the weak (2,0) c4‐X and the (25,0) b′–X transitions, we have measured the effective oscillator strength values with a roughly equal spectral step covering the perturbed features in the 83.422–83.477 nm region. The present results will contribute to a correct interpretation of the OII 83.4 nm EUV airglow emission of the Earth by elucidating the effect of temperature on the atmospheric extinction due to absorption by N2 and O2.

Electronic spectroscopy of the Ã1A″← X̃1A′ system of CDF

To further investigate the Renner-Teller (RT) effect and barriers to linearity and dissociation in the simplest singlet carbene, we recorded fluorescence excitation spectra of bands involving the pure bending levels 2(n)(0) with n = 0-9 and the combination states 1(1)(0)2(n)(0) with n = 1-8 and 2(n)(0)3(1)(0) with n = 0-5 in the A(1)A''<-- X(1)A' system of CDF, in addition to some weak hot bands. The spectra were measured under jet-cooled conditions using a pulsed discharge source, and rotationally analyzed to yield precise values for the band origins and rotational constants; fluorescence lifetimes were also measured to probe for lifetime lengthening effects due to the RT interaction. The derived A state parameters are compared with previous results for CHF and with predictions of ab initio electronic structure theory. The approach to linearity in the A state is evidenced in a sharp increase in the A rotational constant with bending excitation, and a minimum in the vibrational intervals near 2(9). A fit of the vibrational intervals for the pure bending levels yields an A state barrier to linearity in good agreement both with that previously derived for CHF and ab initio predictions. From the spectra and lifetime measurements, the onset of extensive RT perturbations is found to occur at a higher energy than in CHF, consistent with the smaller A constant.

Line intensities of acetylene in the 3- [formula omitted]m region: New measurements of weak hot bands and global fitting

About 170 line intensities of 14 weak parallel hot bands of acetylene have been measured in the 3- μ m region. Absolute values of line intensities are obtained with a mean uncertainty of 10%, except for a few lines of 3 very weak bands (uncertainty up to 20%). Vibrational transition dipole moment and Herman–Wallis coefficients have been determined for each measured band. These measured line intensities together with previously published ones (JQSRT 2005;92:239–60) have been treated simultaneously within the framework of the effective operators approach. Using only 6 effective dipole moment parameters, it was possible to reproduce the 591 measured line intensities of the 20 bands with a root mean square of the residuals equal to 4.2%.

Fourier transform spectra and torsion–rotation structure of the CO-stretching 2 ν8 overtone and 2 ν8– ν8 hot band of CH 3OH

The Fourier transform infrared (FTIR) spectrum of the 2 ν 8 overtone band of the CO-stretching vibrational mode of CH 3OH has been investigated in the 5-μm region at a spectral resolution of 0.0048 cm −1 (1/MOPD) and a higher pressure-path-length product than heretofore. Assignments are reported for high- K 2 ν 8 subbands in the ground state ( n=0) of the ν 12 torsion, and for 2ν 8+ν 12−ν 12 (n=1) and 2 ν 8+2 ν 12−2 ν 12 ( n=2) torsionally excited combination subbands. Upper-state υ 8=2 term values have been fitted to series expansions in powers of J( J+1) to obtain J-independent substate origins defining the torsion- K-rotation structure of the overtone state. Perturbations due to Coriolis and asymmetry resonances have been observed and characterized, as well as J-localized level-crossing resonances arising principally from interactions with the υ 7=2 overtone state of the in plane CH 3-rocking mode and the ( υ 7, υ 8)=(1,1) combination state. Differences between υ 8=2 and υ 8=1 term values have been used to generate a predicted map of the weak 2 ν 8– ν 8 CO-stretching hot band. The hot band underlies the main ν 8 fundamental in the 10-μm region, so is of significance to the determination of the fundamental line intensities. A number of the weak hot-band lines have been observed in the 10-μm FTIR spectrum.

Mid- and Near-Infrared Spectra, Millimeterwave Spectra, and Global Analysis of 16O12C80Se

We have recorded a total of 12 FTIR spectra of monoisotopic OC80Se in different spectral regions with a resolution (1/maximum optical path difference) between 2.7 and 13.2 × 10−3 cm−1. These spectra spanned the range from 350 to 7800 cm−1, many bands being studied with different p × L products in order to also detect weak hot bands. Altogether 18 band systems comprising 81 different bands, mostly of Σ type, were observed and analyzed by means of polynomial expansions in J(J + 1). New rotational transitions of vibrationally excited states as high as 2200 cm−1 with J" 17–25 in the 140–210 GHz and J" 53–58 in the 430–470 GHz millimeterwave regions were measured with the assistance of predictions by the global fit. This fit was performed using a weighted least-squares procedure and employing the whole body of data, and about 100 molecular parameters were determined that describe the energy level of 16O12C80Se with statistical accuracy. Improved highly accurate ground state parameters up to sextic centrifugal distortion terms were obtained by a merge of ground state combination differences and pure rotational data. The v1, v2, v3 polyad interacts anharmonically with the v1 − 1, v2 + p, v3 + q polyads with p + 2q = 4. Moreover, some local crossings with Coriolis interactions between (v1, v2, v3) and (v1 − 1, v2 + 3, v3 + 1) levels were observed and treated perturbationally.

The Ethylene Hot Band Spectrum near 3000 cm−1

A new hot band spectrum of ethylene has been recorded from 2970 to 3015 cm−1at low rotational temperatures in a seeded molecular jet, using vibrational energy transfer from SF6to C2H4. An IR–IR double resonance technique has been applied to pump the lower states and subsequently probe the hot bands. Two new hot bands, ν10+ ν11− ν10and ν7+ ν11− ν7, have been found. The weak hot band starting from ν7has been identified by direct labeling of some rotational levels in the ν7manifold. High resolution FTIR spectra at ambient and at elevated temperatures have been recorded, too; it has thus become possible to extend the analysis to higher rotational quantum numbers. The previously analyzed ν9+ ν10level has been reinvestigated and ab-type Coriolis interaction with the nearby ν7+ ν11state has been observed. Rotational energy levels of ν7+ ν11and of ν9+ ν10have been fitted simultaneously, taking into account the local perturbations due to five dark states. From the shift of allK≠ 0 levels to higher frequencies in the ν10+ ν11state, a globala-type Coriolis interaction with ν8+ 2ν12has been identified.

The CX transition in CaKr + and CaAr +

An electronic transition in the isolated CaKr + ion with an origin at 14217 cm −1 has been observed in the resonant photodissociation spectrum. A short vibrational progression yields excited state vibrational constants of ω′ e = 60 cm −1 and ω e x′ e = 2.78 cm −1 and a diabatic binding energy of 330 ± 100 cm −1. The excited state in this transition arises from the Ca +3 p 63 d[ 2 D] + Kr[ 1 S] atomic limit and is tentatively assigned as a 2 Σ + state. A single weak hot band feature places the ground state vibrational frequency, ΔG″ 1 2 , at 74 cm −1. The analogous transition in CaAr + has also suffered analysis. The X 2 Σ + ground state of the CaKr + ion is bound by 840 ± 100 cm −1 almost the same as that found for CaAr +, 890 ± 100 cm −1.

Near infrared overtone spectroscopy of C2D2

In the near infrared region from 11 800 cm-1 to 12 400 cm-1, the overtone spectrum of dideuteroacetylene has been recorded with a continuously tunable diode laser and a very sensitive detection system. We report new very weak hot bands and their rovibrational constants.

High‐resolution photoacoustic Raman spectroscopy of gases

AbstractA high‐resolution photoacoustic Raman spectroscopy experiment is described. The resolution achieved by using two single‐mode pulsed lasers is about 0.0054 cm−1 (full width at half maximum intensity). The experiment was tested first on the v1/2v2 bands of CO2 and gave an increase of at least about one order of magnitude in the signal‐to‐noise ratio with respect to stimulated Raman spectroscopy at low pressure (ca. 10 Torr ≈ 1.3 kPa). The sensitivity is also demonstrated by the study of the weak hot band v1 + v2 — v2 of CO2. In both cases, the experimental line shape is well reproduced by taking into account Doppler and collisional effects. A comparison with CARS spectra was also made.