A new study of the ν 2(A 1) infrared band of phosphorus trifluoride

The high-resolution Fourier transform infrared spectrum of phosphorus trifluoride (PF₃) has been reinvestigated in the v_2?=?1 vibrational excited state near 487?cm^?1 (at a resolution of 3?×?10^–3?cm^–1). Thanks to our new accurate rotational ground-state C ₀ value, 0.159970436(69)?cm^–1, and to recent pure rotational measurements, 318 new infrared transitions of the ν ₂ fundamental band have been assigned, extending the rotational quantum number values up to K _max?=?71 and J _max?=?72. A merge, for the first time, of 135 reported microwave data (K _max?=?42 and J _max?=?49) within the v_2?=?1 excited level and 2860 rovibrational transitions yielded improved constants of ν ₂. Parameters of this band have been obtained, up to sextic centrifugal distortion constants, by least-squares fits, σ _IR?=?3.60?×?10^–4?cm^–1 and σ _MW?=?5.53?×?10^–6?cm^–1 (166?kHz). Comparison of these constants with those measured previously by infrared spectroscopy reveals orders of magnitude higher accuracy of these new values.     

Far infrared pure rotational spectrum of methylacetylene

The pure rotational spectrum of methylacetylene has been recorded in the far infrared region between 10 and 60 cm^?1 with a Fourier transform spectrometer whose theoretical resolution was 0.025 cm^?1. From the measured wavenumbers it has been possible to determine the rotational constants in the ground state and in the v₅ = 1, v₈ = 1, v₁₀ = 1, 2, 3, 4 levels.     

The high-resolution infrared spectrum of the 201 band of carbonyl fluoride: Determination of the far infrared laser frequencies

The first high-resolution (0.0024 cm^?1) spectrum of the 2₀¹ band of COF₂ at 963 cm^?1 is reported. Nearly 4000 rotational transitions have been observed and assigned in the band between 936 and 990 cm^?1. The line positions are estimated to be accurate to 0.0001 cm^?1 (relative). The spectrum was calibrated using two adjacent bands of OCS. Approximately 1560 infrared transitions have been fitted simultaneously with the previously reported microwave data. The wave numbers of far infrared laser lines recently observed by Tobin and by Temps and Wagner have been calculated from the 2¹ energy levels, with estimated uncertainties of between 10^?5 and 10^?6 cm^?1.     

Submillimeter wave spectrum and molecular constants of N2O

The submillimeter wave spectrum of the N₂O molecule has been investigated within the 375–565 GHz frequency range with a sensitivity better than 10^?8 cm^?1. The measured frequencies include 161 lines with intensities γ ? 10^?6 cm^?1 belonging to 22 spectroscopically different species of the molecule (specifically, the ground and some excited vibrational states of the five most abundant isotopic species of the molecule in natural abundance) with a statisticall and systematic error of the order of magnitude 10^?8. Rotational and two centrifugal stretching constants could be determined for each spectroscopic species. For each isotopic species observed, we have made a general analysis of the spectrum in different vibrational states bearing in mind resonance effects. The total number of the rotational and rovibrational constants obtained exceeds 40.     

Doppler-limited and atmospheric spectra of the 4-μm ν1 + ν3 combination band of SO2

The combination vibration-rotation ν₁+ν₃ band of SO₂ has been recorded under Doppler-limited and atmospheric conditions with 3 × 10^?4 cm^?1 instrumental resolution using a difference-frequency laser. The spectra are compared to recent theories based on rotational constants from microwave data.     

High resolution Raman spectroscopy of the fundamental vibrational band of 16O2

The vibrational Raman spectrum of ¹⁶O₂ has been recorded with high resolution (0.05 cm^?1 for the Q branch). The expansion of the Hamiltonian as a sum of irreducible tensors of the O(3) group allowed us to obtain easily the expressions for the energy levels, taking into account the off-diagonal matrix elements. From the analysis of the spectrum the excited state constants have been calculated; in particular the rotational constants obtained are: B₁ = 1.421884 ± 0.000013 cm^?1 and D₁ = (?4.864 ± 0.014)10^?6 cm^?1.     

Infrared spectrum of sulfur difluoride in the gas phase around 12.5 μm

Gaseous SF₂ was prepared from COS reacting with cooled F₂. The infrared spectrum of SF₂ was recorded with a Nicolet Fourier Transform Spectrometer. Analysis of the spectrum is achieved between 780 and 860 cm^?1. Molecular band parameters (band centers, rotational constants, Coriolis interaction terms, etc.) were derived for both fundamentals ν₁ (838.5299 cm^?1) and ν₃ (813.0413 cm^?1).     

The high-resolution spectrum of ozone between 8 and 150 cm−1

The rotational spectrum of ¹⁶O₃ in the region 8–150 cm^?1 has been measured at high resolution (0.0033 cm^?1 at 30 cm^?1) with a polarizing FT interferometer. From the rotational analysis of the present data (about 1000 transitions) combined with the previously reported millimeterwave data (about 210 transitions), a new set of rotational and centrifugal distortion constants was derived, which reproduces the measured transition frequencies within their accuracy.     

First high-resolution analysis of the 5ν3 band of nitrogen dioxide near 1.3 μm

The first high-resolution absorption spectrum of the 5ν₃ band of the ¹⁴N¹⁶O₂ molecule at 7766.071 cm^?1 was recorded by high sensitivity CW-Cavity Ring Down Spectroscopy between 7674 and 7795 cm^?1. The noise equivalent absorption of the recordings was α_min≈1×10^?10 cm^?1. The assignments involve energy levels of the (0,0,5) vibrational state with rotational quantum numbers up to K_a=9 and N=47. The set of the spin–rotation energy levels were reproduced within their experimental uncertainty using a theoretical model, which takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,5) vibrational state and those of the (0,2,4) dark state together with the electron spin–rotation resonances within the (0,0,5) and (0,2,4) states. Precise values were determined for the (0,0,5) vibrational energy rotational, spin-rotational constants and for the (0,2,4)?(0,0,5) coupling constants. In addition the (0,2,4) rotational and spin-rotational constants were estimated. Using these parameters and the value of the transition dipole moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 5ν₃ band was generated and is provided as Supplementary material.     

Far-infrared rotational spectra of some freons; chlorotrifluoromethane,dichlorodifluoromethane, and trichlorofluoromethane

The far-infrared rotational spectra of chlorotrifluoromethane, dichlorodifluoromethane, and trichlorofluoromethane have been observed with an interferometric (Fourier transform) spectrometer in the region 10–40 cm^?1 at a resolution of 0.07 cm^?1. CCl₂F₂ exhibits a continuum spectrum at this resolution, but symmetric top rotational fine structure is observed for CClF₃ and CCl₃F. Isotope splitting is also observed in CClF₃, and analysis yields the rotational constants for C³⁵ClF₃ of B₀ = 0.11112 cm^?1, D_J = 1.6 × 10^?8cm^?1; and for C³⁷ClF₃, B₀ = 0.10835 cm^?1, D_J = 1.5 · 10^?8cm^?1. Isotopic shifts can be allowed for in CCl₃F to yield constants for C³⁵Cl₃F of B₀ = 0.0821 cm^?1, D_J = 1 × 10^?8cm^?1. These values are all in agreement with those deduced from microwave studies of the low J transitions apart from B₀ for C³⁵ClF₃, where the difference is outside the expected experimental error.     

The vibration-rotation HDO absorption spectrum between 8558 and 8774 cm−1

The absorption spectrum of HDO has been recorded in the region 8558–8774 cm^?1 using a high-sensitivity intracavity F₂^?:LiF center laser spectrometer. The absorption sensitivity is 10^?7 cm^?1 and the line-center determination accuracy is about 4 × 10^?2 cm^?1. The spectrum was interpreted and the absorption lines were attributed to the ν₂ + 2ν₃ band of HDO. Energy levels up to J = 12 and rotational and centrifugal parameters of the vibrational (012) state were obtained.     

Carbon suboxide: The infrared spectrum from 1800 to 2600 cm−1

The infrared spectrum of carbon suboxide has been recorded from 1800 to 2600 cm^?1 at a resolution of 0.003 cm^?1. About 7% of the ca. 40 000 lines observed have been assigned and analyzed, belonging to 36 different bands. Most of these are associated with the fundamental ν₃, at 2289.80 cm^?1, and the combination band ν₂ + ν₄, at 2386.61 cm^?1, each of which give rise to a system of sum bands, difference bands, and hot bands involving the low-wave-number fundamental ν₇ at 18 cm^?1. A few other tentative assignments are made. The bands have been analyzed for vibrational and rotational constants.     

Infrared spectrum of CO2 in the region of the bending fundamental ν2

The infrared spectrum of CO₂ in the region 540–830 cm^?1 has been studied with a Fourier spectrometer at a resolution of 0.010 cm^?1. In addition to the fundamental ν₂, more than 10 “hot” band transitions of ¹²C¹⁶O₂ have been identified. The rotational constants involved have been derived. Special care has been taken in obtaining accurate constants for the level 01¹0. The ν₂ fundamentals of the isotopic molecules ¹³C¹⁶O₂, ¹⁶O¹²C¹⁸O, and ¹⁶O¹²C¹⁷O have also been observed in a natural sample.     

Assignments of the high-resolution infrared spectrum of the ν1 band of D14N3

An infrared absorption spectrum of the ν₁ band of D¹⁴N₃ has been measured with a resolution of 0.005 cm^?1. Seven ΔK_A = 0 subbands have been observed, and the rotational structure of each band has been assigned and analyzed to give effective rotational constants and values for the subband origins.     

The 2ν2, ν1 and ν3 bands of D216O. The ground state (000) and the triad of interacting states {(020), (100), (001)}

Three spectra of D₂¹⁶O between 2170 and 3090 cm^?1 have been recorded with a Fourier transform spectrometer having a resolution of about 5 × 10^?3 cm^?1. A careful analysis of the bands 2ν₂, ν₁, and ν₃ has led to a largely extended and more precise set of rotational levels belonging to the vibrational states (000), (020), (100), and (001). From this set, we have then been able to determine improved rotational constants for the ground state (000) and precise vibrational energies, rotational and coupling constants for the three interacting states (020), (100), and (001). The Fermi-type interaction between (020) and (100) as well as the Coriolis-type interactions between (100) and (001) and between (020) and (001) have been explicitly taken into account. Many vibrorotational resonances were detected and are discussed.     

The stretching fundamental bands of 13C2D2

The stretching fundamental bands of the isotopically substituted acetylene ¹³C₂D₂ have been recorded and analysed. The Raman spectra of the Q branch of v ₁ and v ₂, Σ⁺ _g -Σ⁺ _g bands, have been recorded with an instrumental resolution of about 3.0 x 10^?3 cm^?1 using inverse Raman spectroscopy. The infrared spectrum has been recorded in the region between 2350 cm^?1 and 2500 cm^?1 with an instrumental resolution of 4.0 x 10^?3 cm^?1. Transitions belonging to the v ₃, Σ⁺ _u -Σ⁺ _g , fundamental band have been identified and assigned. The vibrational energies and the rotational and centrifugal distortion constants of the excited states of all the observed transitions have been determined. The molecular parameters obtained reproduce the assigned wave-numbers with a standard deviation of the same order of magnitude as the experimental uncertainty.     

High-resolution infrared spectrum of CH2D2: The ν9 fundamental band at 8 u̧m

The infrared spectrum of CH₂D₂ has been recorded between 1100 and 1360 cm^?1 with a SISAM-type spectrometer whose resolution limit is about 0.015 cm^?1 in our spectrum. Some lines have been identified as transitions of the ν₃ parallel band of CH₃D. The band center ν = 1236.2786 ± 0.0010 cm^?1 and a set of upper state constants was obtained for the ν₉ band of CH₂D₂. A perturbation was pointed out in ν₉; nevertheless, all frequencies have been fitted with a standard deviation of 3.8 × 10^?3 cm^?1.     

DFT molecular structure and initial assignment for the FTIR spectrum of ν7 band of nitromethane-D3

The preliminary analysis of the DFT calculations and the high-resolution Fourier transform spectrum of the ν₇ band of CD₃NO₂ have been carried out for the first time. The rotational structure up to J = 10 have been fitted using Watson’s A-reduction in I ^r representation with a standard deviation of 0.0048cm⁻¹. The rotational constants A, B, C have been obtained for the ν₇ state of CD₃NO₂ with good statistical significance.     

Infrared laser velocity modulation spectrum of the ν3 fundamental band of HBCI+

The infrared spectrum of the ν₃ fundamental band of HBC1⁺ has been observed using the velocity modulation detection technique. The ion was produced in an ac glow discharge containing a mixture of H₂ and BC1₃. Thirty-two transitions of the fundamental band of the most naturally abundant isotopomer, H¹¹B³⁵C1⁺, between 1105 and 1170cm^?1 have been assigned. The ν₃ band origin and rotational constants have been determined to be ν₀ = 1121.5677(20)cm^?1, B ₀ = 0.63089(23)cm^?1 and B ₁ = 0.62699(21)cm^?1. A second series of lines have been attributed to the H¹¹B³⁷C1⁺ isotopomer, although it has not been possible to make an unambiguous J assignment of these lines.     

Measurement and analysis of the ν2 band of D216O

The rotational structure of the ν₂ band of D₂¹⁶O between 700 and 1550 cm^?1 has been analyzed from spectra recorded with a Fourier transform spectrometer (nominal resolution: 0.1 cm^?1). By applying Watson's reduced Hamiltonian and a least squares method to the set of observed transitions, together with microwave data and the infrared data of Williamson, 22 rotational constants for the ground state and 17 for the upper state have been obtained which predict the positions of more than 700 observed lines with a standard deviation of 0.04 cm^?1.