Fundamental Ν3 Research Articles

High Resolution Rovibrational Spectroscopy of the ν6 and ν3 + ν7 Bands of H2CCCH.

The molecular ion H2CCCH+ has been further investigated in a 4 K cryogenic ion trap instrument employing the leak-out spectroscopy (LOS) method. Transitions within two perpendicular bands, the fundamental ν6 (antisymmetric H-C-H stretch) and the combination band ν3 + ν7 (C≡C stretch and CH2 rock), have been measured in high resolution for the first time. The spectral analysis was aided by high level quantum chemical calculations and by our previous study of the parallel ν1 and ν3 + ν5 bands [Silva, W. G. D. P. ; Mol. Phys. 2023, e2296613]. The novel results presented here have allowed for a seventy-fold improvement on the accuracy of the value of the A0 rotational constant of this near-prolate asymmetric top.

Collision-broadening of vibration-inversion-rotation ammonia spectral lines in Q(J)-branch at 6.2 µm by cavity ring-down spectroscopy

In this experimental investigation, collision broadening effects on the Q(J)-branch vibration-inversion-rotation spectral lines of ammonia (NH3) within the fundamental ν4 asymmetric bending vibrational band in the 6.2 µm mid-IR region are reported. A continuous-wave external-cavity quantum cascade laser coupled with a high-sensitive cavity ring-down spectrometer was employed to selectively probe 10 transitions in high-resolution, including few inversion doublets of gaseous NH3. Pressure-broadening coefficients, γNH3-Xi (Xi = He, Ar, N2, O2, zero-air) in cm−1 atm−1, characterizing the collision interaction between NH3 and various external perturbing gases, including helium, argon, nitrogen, oxygen, and zero-air, were determined at room temperature (296 K). Mean collision times and optical collision diameters of each collision partner were explored to gain deeper insight into the perturber-induced collision dynamics. This investigation elucidates the intricate intermolecular interactions and collision phenomena induced by various foreign perturbers with NH3, with potential implications for future spectroscopic and atmospheric research of this polyatomic molecule.

Reinvestigation of the ν3-ν6 Coriolis interaction in trifluoroiodomethane.

The lowest-frequency fundamental ν6 of trifluoroiodomethane (CF3I) has never been directly observed and analyzed at high resolution in the gas phase. The ν6(e) level interacts with ν3(a1) at 286.297 cm-1via a b-axis Coriolis interaction, which perturbs the rotational structure of both levels. In this work, we report low-J microwave transitions (for J ranging from 0-2) within the ν6 vibrational level. The l-type doubling observed in our spectrum agreed poorly with the predictions of previously published models of the interacting ν3-ν6 levels, prompting us to refine the model. We performed ab initio anharmonic force-field calculations, which were used to constrain some of the parameters, and which served as a check on some of the floated parameters. We fit a dataset consisting of 3593 transitions, which combined our measurements with previous microwave, millimeter wave, and high-resolution infrared observations. A reasonable set of fit parameters is obtained with ν6 = 267.28 cm-1, but we cannot rule out a lower value of ν6 = 261.5 cm-1 consistent with analyses of the vibrational level structure.

Spectral mosaics: Composite absorption cross sections of air-broadened tetrafluoromethane with comparable uncertainty in the measured intensity over orders of magnitude

We have obtained low-uncertainty absorption cross sections, together with explicit uncertainties for every wavenumber, for mixtures of tetrafluoromethane (CF4) with air at 296 K. The integrated intensities in the region of the two fundamental bands ν3 and ν4 as well as four combination bands, namely ν1 + ν4, ν2 + ν4, ν3 + ν4, and ν2 + ν3, were also evaluated. The expanded uncertainties are below 1.3 % for the fundamental and below 3 % for the combination bands. An intensity estimation for the forbidden ν1 band is also obtained. Spectral data is available online: doi: 10.7795/720.20230920.

Ab Initio Rovibrational Spectroscopy of the Acetylide Anion.

In this work the rovibrational spectrum of the acetylide anion HCC- is investigated using high-level electronic structure methods and variational rovibrational calculations. Using a composite approach the potential energy surface and dipole surface is constructed from explicitly correlated coupled-cluster accounting for corrections due to core-valence correlation, scalar relativistic effects and higher-order excitation effects. Previous approaches for approximating the latter are critically evaluated. Employing the composite potential, accurate spectroscopic parameters determined from variational calculations are presented. In comparison to the few available reference data the present results show excellent agreement with ground state rotational constants within 0.005% of the experimental value. Intensities determined from the variational calculations suggest the bending fundamental transition ν2 around 510 cm-1 to be the best target for detection. The rather weak CD stretching fundamental ν1 in deuterated isotopologues show a second-order resonance with the (0,20,1) state and the consequences are discussed in some detail. The spectroscopic parameters and band intensities provided for a number of vibrational bands in isotopologues of the acetylide anion should facilitate future spectroscopic investigations.

The 2ν3/ν2/ν5/ν3 + ν6 band system of CH3Br revisited: Anharmonic and Coriolis interactions in a four-level system near 1400 cm−1

The infrared spectrum of gaseous methyl bromide (CH3Br) in natural abundance has been analyzed with high resolution, between 1150 and 1700 cm−1. In this spectral region, two fundamental bands, ν2 (A1) and ν5 (E), an overtone 2ν3 (A1) and a combination band ν3 + ν6 (E) occur. The novelty of the present study consists in considering, besides the strong Coriolis and α-interactions coupling the v2 = 1 and v5 = 1 levels, a large variety of anharmonic and rovibrational interactions involving also the v3 = 2 and v3 = v6 = 1 levels. For this latter level, the data set belonging to the ν3 + ν6 combination band has been extended with respect to previous work of Ouahman et al. [Spectrochim. Acta45A (1989) 175–179], to about thousand assigned transitions with -6≤K·ΔK≤+16. Thanks to the completeness of the theoretical model, the global standard deviation of the reproduction of the experimental wavenumbers in the ν2/ν5 system was greatly improved with respect to the previous high-resolution study of Kwabia Tchana et al. [J. Mol. Spectrosc.228 (2004) 441–452]. For this Coriolis-interacting band system, two different reduction schemes, according to the theory of Stříteská et al. [J. Mol. Spectrosc.256 (2009) 135–140], were applied and were proved to be equally successful.

Line positions and intensities of the ν1 band of 12CH3I using mid-infrared optical frequency comb Fourier transform spectroscopy

We present a new spectral analysis of the ν1 and ν3+ν1−ν3 bands of 12CH3I around 2971 cm−1 based on a high-resolution spectrum spanning from 2800 cm–1 to 3160 cm–1, measured using an optical frequency comb Fourier transform spectrometer. From this spectrum, we previously assigned the ν4 and ν3+ν4−ν3 bands around 3060 cm–1 using PGOPHER, and the line list was incorporated in the HITRAN database. Here, we treat the two fundamental bands, ν1 and ν4, together with the perturbing states, 2ν2+ν3 and ν2+2ν6±2, as a four-level system connected via Coriolis and Fermi interactions. A similar four-level system is assumed to connect the two ν3+ν1−ν3 and ν3+ν4−ν3 hot bands, which appear due to the population of the low-lying ν3 state at room temperature, with the 2ν2+2ν3 and ν2+ν3+2ν6±2 perturbing states. This spectroscopic treatment provides a good global agreement of the simulated spectra with experiment, and hence accurate line lists and band parameters of the four connected vibrational states in each system. It also allows revisiting the analysis of the ν4 and ν3+ν4−ν3 bands, which were previously treated as separate bands, not connected to their ν1 and ν3+ν1−ν3 counterparts. Overall, we assign 4665 transitions in the fundamental band system, with an average error of 0.00071 cm–1, a factor of two better than earlier work on the ν1 band using conventional Fourier transform infrared spectroscopy. The ν1 band shows hyperfine splitting, resolvable for transitions with J ≤ 2 × K. Finally, the spectral intensities of 65 lines of the ν1 band and 7 lines of the ν3+ν1−ν3 band are reported for the first time using the Voigt line shape as a model in multispectral fitting. The reported line lists and intensities will serve as a reference for high-resolution molecular spectroscopic databases, and as a basis for line selection in future monitoring applications of CH3I.

Dual mid-infrared wavelength Faraday rotation spectroscopy NOx sensor based on NdFeB ring magnet array

Faraday rotation spectroscopy (FRS) exploits the magneto-optical Faraday rotation effect to achieve highly sensitive detection of paramagnetic molecules. Most of the currently reported FRS sensors suffer from high power consumption, while enabling detection of only a single component. In this work, a novel dual mid-infrared wavelength FRS sensor is proposed that enables the simultaneous detection of two paramagnetic molecules (nitrogen oxides, NOx = NO + NO2) in a single absorption cell. A neodymium-iron-boron (NdFeB) ring magnet array was designed to replace the solenoid coil to provide a stable, power-free magnetic field. The magnetic induction line distribution characteristics around the permanent magnets were analyzed based on the finite element method. Two mid-infrared quantum cascade lasers were used to detect the strongest fundamental ν2 rotational-vibrational band of NO (1875.81 cm−1) and the ν3 fundamental band of NO2 (1613.25 cm−1), respectively. A dual-wavelength Herriott cell (DWHC) is coaxially combined with a NdFeB ring magnet array to amplify the interaction of the laser beam with paramagnetic NOx molecules in an axial magnetic field. This low-power FRS NOx sensor achieves minimum detection limits of 0.58 ppb and 0.95 ppb for NO2 and NO, respectively, over an optical length of 23.7 m.

Herman-Wallis factor for a molecule of type HCN

We suggest a novel theoretical approach to calculate Herman-Wallis factors in rovibrational spectra of non-centrosymmetric linear molecules possessing a permanent dipole. A fresh glance allowed to extend the theory recently formulated in [K.V. Kazakov and A.A. Vigasin, Phys. Rev. A, 104, 042805 (2021)]. Our obtained expressions for the first Herman-Wallis correction factors result in evaluation of the rovibrational interaction impact on the line intensities belonging to fundamental modes ν1,ν2, and ν3 for H12C14N, H13C14N, H12C15N, D12C14N, D13C14N, and D12C15N. As an auxiliary outcome, the sum rule for the Coriolis constants is generally derived in detail.

Infrared frequency comb spectroscopy of CH2I2: Influence of hot bands and pressure broadening on the ν1 and ν6 fundamental transitions.

Direct frequency comb spectroscopy was utilized to measure the vibrational absorption spectrum of diiodomethane, CH2I2, from 2960 to 3125cm-1. The data were obtained using a CH2I2 concentration of (6.8 ± 1.3) × 1015moleculecm-3 and a total pressure of 10-300mbar with either nitrogen or argon as the bath gas. The rovibrational spectra of two fundamental transitions, ν6 and ν1, were recorded and analyzed. We suggest that a significant contribution to the observed congested spectra is due to the population in excited vibrational states of the low energy ν4 I-C-I bend, resulting in transitions 61 04n n and 11 04n n, where the integer n is the initial vibrational level v = 1-5. PGOPHER was used to fit the experimental spectrum, allowing for rotational constants and other spectral information to be reported. In addition, it was found that the peak widths for the observed transitions were limited by pressure broadening, resulting in a pressure broadening parameter of (0.143 ± 0.006) cm-1 atm-1 by N2 and (0.116 ± 0.006) cm-1 atm-1 by Ar. Further implications for other dihaloalkane infrared spectra are discussed.

Revised assignments of the v4=1 vibrational level of CH35Cl3: The ν4 and ν4-ν3 rovibrational bands with remarkable clustering effects

The v4 = 1 fundamental vibration of chloroform (C-H bending vibration, E symmetry) has been reinvestigated at high-resolution. For this purpose, FTIR spectra recorded in the regions of the ν4 (1220 cm−1) and ν4 − ν3 (853 cm−1) bands were employed. Spectra were recorded at the Synchrotron Soleil, using a monoisotopic CH35Cl3 sample. More than 6900 transitions were assigned, among which more than 4200 in the difference band. Assignments span the 0 ≤ J ≤ 100 and − 75 ≤ K′′ΔK ≤ 75 values, despite the systematic overlaps of transitions, observed over a wide range of the spectrum. These overlaps, giving rise to remarkable clustering effects, are characteristic of both the fundamental ν4 and the difference ν4-ν3 bands. They are also, sometimes, source of misassignments, especially when the systematic use of the lower state combination differences as a checking is not possible. In this regard, we have to notice here that the indirect assignment checking through fundamental and difference transitions sharing a common upper level allowed us to systematically correct and extend the K-assignments of the rRK(J) transitions in the ν4 band.In the least-squares fit, the ground state parameters were fixed to the most recent experimental values. The parameters of the v3 = 1 level could be refined and improved with respect to previous determination, thanks to about 800 IR data collected from a FTIR spectrum of the ν3 band, together with more than 1300 MMW data in the v3 = 1 level (22 ≤ J ≤ 98 and 0 ≤ K ≤ 79).The theoretical model used for the v4 = 1 fundamental vibration is that of an isolated vibrational level, and ten molecular parameters were refined; the global standard deviation of the fit was of 0.160 × 10−3 cm−1, which is of the order of the accuracy of the experimental data.

High-Resolution spectroscopy and analysis of the fundamental modes of [formula omitted]Si[formula omitted]. Accurate experimental determination of the Si[formula omitted]F bond length

Silicon tetrafluoride (SiF4) is a trace component of volcanic gases and is gaining industrial importance. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. Following a previous reinvestigation of the ν3 and ν4 fundamentals (Richard et al. 2021), we have undertaken an extensive high-resolution study of its infrared absorption bands. We present here an update of this study. It features the recording of new far-infrared spectra, taking advantage of synchrotron radiation, and a global fit giving a consistent parameter set for the ground and fundamental states of 28SiF4, now including the v1=1 and v2=1 states, by adding to the global analysis the newly measured ν2, ν1−ν4, and ν4−ν2 bands near 264, 412, and 125 cm−1, respectively. Nearly 20000 assigned lines pertaining to seven distinct rovibrational bands were fitted with an excellent accuracy (global standard deviation of 0.296). This allows us to obtain an accurate experimental value for the Si−F bond length, re(SiF4)=1.5516985(30) Å. Some new band intensity estimates allow us to update our SiF4 calculated spectroscopic database.

Analysis of the High-Resolution Spectrum of Molecules in Doublet Electronic States: Fundamental ν3 Band of Chlorine Dioxide (16O35Cl16O) in the Ground Electronic State X 2B1

Analysis of the High-Resolution Spectrum of Molecules in Doublet Electronic States: Fundamental ν3 Band of Chlorine Dioxide (16O35Cl16O) in the Ground Electronic State X 2B1

High-Resolution Infrared Spectroscopy of DC3N in the Stretching Region

The perspectives opened by modern ground-based infrared facilities and the forthcoming James Webb Telescope mission have brought a great attention to the ro-vibrational spectra of simple interstellar molecules. In this view, and because of the lack of accurate spectroscopic data, we have investigated the infrared spectrum of deuterated cyanoacetylene (DC3N), a relevant astrochemical species. The ν1, ν2, and ν3 fundamentals as well as their hot-bands were observed in the stretching region (1,500–3,500 cm−1) by means of a Fourier transform infrared spectrometer. Supplementary measurements were performed at millimeter-wavelengths (243–295 GHz) with a frequency-modulation spectrometer equipped with a furnace, that allowed to probe pure rotational transitions in the investigated stretching states. Furthermore, since HC3N is observed as by-product in our spectra and suffers from the same deficiency of accurate infrared data, its ro-vibrational features have been analyzed as well. The combined analysis of both rotational and ro-vibrational data allowed us to determine precise spectroscopic constants that can be used to model the infrared spectra of DC3N and HC3N. The importance of accurate molecular data for the correct modeling of proto-planetary disks and exoplanetary atmospheres is then discussed.

The Raman jet spectrum of trans-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database.

Revisiting recently published Raman jet spectra of monomeric formic acid with accurate high order perturbative calculations based on two explicitly correlated coupled-cluster quality potential energy surfaces from the literature, we assign and add 11 new vibrational band centers to the trans-HCOOH database and 53 for its three deuterated isotopologs. Profiting from the synergy between accurate calculations and symmetry information from depolarized Raman spectra, we reassign eight literature IR bands up to 4000 cm-1. Experimental detection of highly excited torsional states (ν9) of trans-HCOOH, such as 4ν9 and ν6 + 2ν9, reveals substantial involvement of the C-O stretch ν6 into the O-H bend/torsion resonance ν5/2ν9, which is part of a larger resonance polyad. Depolarization and isotopic C-D substitution experiments further elucidate the nature of Raman peaks in the vicinity of the O-H stretching fundamental (ν1), which seem to be members of a large set of interacting states that can be identified and described with a polyad quantum number and that gain intensity via resonance mixing with ν1.

Universal Function for the Calculation of Broadening of Absorption Lines of the H2S Molecule by Monoatomic Gases

A universal analytical model is proposed for calculating coefficients γ of broadening of absorption lines of the H2S molecule by inert gas atoms A (helium, neon, argon, krypton, and xenon). In this model, only one parameter depends on the broadening atom A; other parameters are common for all atoms. This parameter determines the ratio γ(A)/γ(A′) for the A and A′ atoms. The model parameters are determined from values of γ calculated for the fundamental bands ν1, ν2, and ν3 of the H2S molecule, as well as from known experimental values of γ. Values of γ calculated using the model are compared with available experimental data. For some lines from the ν1 and ν3 bands, there is a significant discrepancy between the experiment and calculation.

Raman spectroscopy study of acetonitrile at low temperature.

We report the low-temperature studies of liquid CH3CN by Raman spectral measurements at ambient pressure with decreasing the temperature from 20 to -196°C. Detailed internal modes especially the lattice modes analysis revealed that the structural phase transitions of acetonitrile from liquid to solid phase β and solid phase β to solid phase α were occurring at -50 and -60°C, respectively. Further, the Fermi resonance parameters between the fundamental ν2 and combination (ν3+ν4) of CH3CN at different temperatures were calculated based on the Bertran's equations. It is found that the Fermi resonance parameters as a function of temperature become discontinued at -50 and -60°C, which coincides with discontinuities observed in the Raman shifts of CH3CN at -50 and -60°C. The results suggest that the Fermi resonance parameters could be used as an indicator to assess the structural phase transition for CH3CN under low temperature.

Mid-IR spectra of the M-type Mira variable R Tri observed with theSpitzerIRS

ABSTRACTWe present analysis of mid-infrared (IR) spectra of the oxygen-rich Mira variable R Tri. The data were taken with the Spitzer Infrared Spectrometer (IRS) as part of a study tracking how Mira variables’ regular pulsations affect circumstellar envelopes. We detected strong emission lines at 13.87, 16.18, and 17.6 $\hbox{$\mu $m}$, and one strong absorption feature at 14.98 $\hbox{$\mu $m}$. The emission features at 13.87 and 16.18 $\hbox{$\mu $m}$ are excited vibrational bands of CO2, while the absorption feature is the fundamental ν2 band. The 17.6 $\hbox{$\mu $m}$ emission feature has a completely different character than the molecular lines and we report its identification as Fe i fluorescence. We used a two-slab model with the radiative transfer code radex to model the CO2 Q-branch bandheads. Our results indicate a slab of gas with T∼600 K located at ∼3–4 R*. The cool temperature discrepancy with the radius provides observational evidence for the previously theoretical ‘refrigeration zone’.

Gas-Phase Isotopic Fractionation Study of Singly and Doubly Deuterated Isotopologues of Water in the H-D Exchange Reaction by Cavity Ring-Down Spectroscopy.

The underlying mechanisms of the triple-oxygen (16O, 17O, and 18O) isotopic content of deuterated (D) isotopologues of water in H-D exchange reactions in the gas phase remain elusive. Herein, we have demonstrated a high-resolution gas-phase spectral analysis of doubly (D2O) and singly (HDO) deuterated isotopologues of water in the region around 7.8 μm using quantum cascade laser-based cavity ring-down spectroscopy. Isotopic fractionations among doubly and singly deuterated species of water, D216O, HD16O, HD17O, and HD18O, in the gas phase were carried out by probing the fundamental and hot band transitions in the ν2 (bending) mode of D2O and the fundamental ν2 transitions for the other water isotopes. We subsequently investigated the fractionations of different D-enriched water isotopologues for the H-D exchange reaction using various mixtures of D2O in H2O. We explored the potential role of triple-oxygen isotopic contents through enrichments and depletions of HD16O, HD17O, and HD18O, involved in the H-D reaction. Our first clear, direct, and quantitative experimental evidence reveals a new picture of gas-phase isotopic fractionation chemistry in a mixture of light and heavy water (H2O-D2O).

First Investigation of the Inversion Rovibrational Spectrum of the 15NHD2 Molecule in the Region from 1100 to 1350 cm–1: the Fundamental ν5 Band

The high-resolution spectrum of the 15NHD2 molecule recorded in the Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA), Paris Diderot University, France, is studied. An analysis is based on the method of ground state combination differences. As a result of the analysis of two inversion vibrational (v5 = 1, s) and (v5 = 1, a) states, more than 1300 rovibrational transitions have been assigned, and about 150 upper vibrational energy levels have been determined.