High-resolution infrared spectrum of CHD279Br: ro-vibrational analysis of the ν5 and ν9 fundamentals

ABSTRACT

The high-resolution infrared spectrum of CHD₂⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 700–900?cm^?1 at an unapodized resolution of 0.0035?cm^?1. This spectral region is characterised by the absorptions of the ν₅ (814.5185?cm^?1) and ν₉ (716.9649?cm^?1) fundamental bands, corresponding to H–C–Br deformation and CD₂ rocking modes, respectively. The ν₅ vibration of symmetry species A^′ gives rise to an a-/c-hybrid band with a predominant a-type component, while the ν₉ mode of A^′′ symmetry produces a b-type envelope. The spectral analysis resulted in the identification of 5290 (J^′?≤?63 and K_a^′?≤?13) and 1657 (J^′?≤?53 and K_a^′?≤?12) transitions for ν₅ and ν₉ bands, respectively. The assigned data were fitted using the Watson’s S-reduced Hamiltonian in the I^r representation and the v₅?=?1 and v₉?=?1 state parameters up to the quartic centrifugal distortion terms have been obtained. From spectral simulations the dipole moment ratio |Δμ_a/Δμ_c| of the ν₅ band has been determined to be 1.4?±?0.1 while the intensity ratio between ν₅ and ν₉ fundamentals has been estimated to have a value of 4.3?±?0.5.     

High-resolution infrared and ab initio investigation of CHD2 79Br: Ro-vibrational analysis of the ν6 fundamental and the 2ν6−ν6 hot band

The high-resolution infrared spectrum of CHD₂ ⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 540–615?cm^?1 at an unapodised resolution of 0.0035?cm^?1. This spectral region is characterised by the ν₆ fundamental (584.8510?cm^?1), corresponding to C–Br stretching mode, and its hot band 2ν₆?ν₆ (578.4333?cm^?1). The spectral analysis resulted in the identification of 3430 transitions (J’?≤?73 and K'_a ?≤?18) for the ν₆ fundamental and 1212 transitions (J’?≤?49 and K'_a ?≤?11) for the hot band 2ν₆?ν₆. The assigned data have been fitted using the Watson’s S-reduced Hamiltonian in the I^r representation and new constants for the ground state from about 24,600 combination differences and sets of parameters for the v ₆?=?1 and 2 vibrational states have been obtained. From spectral simulations the intensity ratio between 2ν₆?ν₆ and ν₆ has been estimated to be 0.15?±?0.02. High-quality ab initio calculations have also been performed at the CCSD(T) level of theory in order to support the experimental investigation through the calculation of molecular parameters relevant to ro-vibrational spectroscopy.     

High resolution FTIR spectroscopy of CH2DF: analysis of the v 3 and v 4 interacting bands

The high resolution (0.004cm^?1) Fourier transform infrared spectrum of the monodeuterated form of methyl fluoride, CH₂DF, has been recorded and analysed in the v ₃ and v ₄ band region around 1420cm^?1. Both bands, coming from A′ symmetry vibrations, have a/b hybrid character, although in v ₃ the b-type component prevails over the a-type. The rotational structure has been analysed using a dyad model including c-type Coriolis coupling and high order vibrational resonance between these states. Accurate upper state molecular parameters and interaction terms have been obtained by fitting about 3270 assigned transitions to Watson's A-reduced Hamiltonian in the I^r representation. In addition, from a simultaneous fit of ground state combination differences coming from this analysis and 42 literature microwave transitions, an improved and more complete set of ground state constants, including three new sextic centrifugal distortion terms (Φ_JK, Φ_KJ and Φ_K), has been derived.     

The infrared spectrum of DCCF in the 320–850 cm−1 region: bending states up to υ4+υ5 = 3

Infrared spectra of deuterated monofluoroacetylene, DCCF, have been recorded in the region between 320 and 850 cm^?1 at an effective resolution ranging from 0.0024 to 0.0031 cm^?1. In total, 6650 rotation vibration transitions were assigned to 37 bands involving the bending states with v₄ + v₅ and |l₄+l₅|, respectively, up to 3, allowing the characterisation of the ground state and of 18 vibrationally excited states. The vν₅ bending fundamental has been studied for the first time. In addition, the difference band v₃ ← v₄ has been detected and analysed. All the assigned transitions have been fitted simultaneously by adopting a model Hamiltonian that takes into account the vibration and rotation l?type resonances. Rotational transitions in the ground and in bending excited states reported in the literature have been included in the global analysis. The set of 57 derived spectroscopic parameters reproduces 6130 infrared and 90 microwave and millimetre?wave transitions satisfactorily with root mean square values of 5.3 × 10^?4 cm^?1 and 77 kHz, respectively.     

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.     

High-resolution FTIR spectrum of vinyl chloride: rovibrational analysis of the v 10 and v 11 fundamental bands

The Fourier transform gas-phase infrared spectra of the v ₁₀ and v ₁₁ bands of natural CH₂=CHCl have been measured with a resolution of 0.005 cm^?1 in the frequency range 820–1010 cm^?1. These vibrations of symmetry species A″ give rise to c-type bands and the transitions observed are characterized by δK _a = ±1 and δK _c = 0, ±2. Both J and K structures have been resolved in different subbranches and about 1800 (J ≤ 64, K _a ≤ 13) and 2800 (J ≤ 72, K _a ≤ 14) transitions for the v ₁₀ and v ₁₁ fundamentals, respectively, have been identified for the ³⁵Cl isotopomer. Combined analysis of the assigned data with the available ground state constants allowed the determination of the band origins, rotational and centrifugal distortion parameters for the v ₁₀ = 1 and v ₁₁ = 1 excited states of CH₂=CH³⁵Cl isotopic species. The molecular constants obtained account for slight perturbations in the v ₁₀ vibrational level.     

The infrared spectrum of 13C2H2 in the 60–2600 cm−1 region: bending states up to v 4 + v 5 = 4

The vibration–rotation spectra of ¹³C substituted acetylene, ¹³C₂H₂, have been recorded in the region between 60 and 2600?cm^?1 at an effective resolution ranging from 0.001 to 0.006?cm^?1. Three different instruments were used to collect the experimental data in the extended spectral interval investigated. In total 9529 rotation vibration transitions have been assigned to 101 bands involving the bending states up to v _tot?=?v ₄?+?v ₅?=?4, allowing the characterization of the ground state and of 33 vibrationally excited states. All the bands involving states up to v _tot?=?3 have been analyzed simultaneously by adopting a model Hamiltonian which takes into account the vibration and rotation l-type resonances. The derived spectroscopic parameters reproduce the transition wavenumbers with a RMS value of the order of the experimental uncertainty. Using the same model, larger discrepancies between observed and calculated values have been obtained for transitions involving states with v _tot?=?4. These could be satisfactorily reproduced only by adopting a set of effective constants for each vibrational manifold, in addition to the previously determined parameters, which were constrained in the analysis.     

The ro-vibrational analysis of the v4 fundamental band of CF3Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

The v₄ fundamental band of CF₃⁷⁹Br and CF₃⁸¹Br, present in natural isotopic abundance, was investigated in the 8.3-μm region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5–1205.0 cm^?1, 1208.0–1210.1 cm^?1 and 1212.5–1214.5 cm^?1. The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm^?1. A Fourier transform infrared spectrum covering the entire spectral region of the v₄ band, between 1190 and 1220 cm^?1, was recorded at 298 K with a resolution of 0.004 cm^?1. The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v₄. In total, 4651 transitions were assigned to CF₃⁷⁹Br, 4047 to CF₃⁸¹Br, with J″_max? = K″_max?=80; of these, 3171 for CF₃⁷⁹Br and 2755 for CF₃⁸¹Br are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C_3v symmetry. The v₄ band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v₄ = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v₄ = 1 for CF₃⁷⁹Br and CF₃⁸¹Br were obtained. The bromine isotopic splitting amounts to 6.9 × 10^?3 cm^?1. In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.     

High resolution study of the v 7 + v 8 band of ethylene (C2H4) at 1889 cm-1

The v ₇ + v ₈ A-type band of C₂H₄ has been recorded between 1932 and 1847 cm^-1 with a resolution of 0·06 cm^-1. The transitions with K _-1 ? 8> and J ? 2>5 have been assigned. Although slight Coriolis resonances perturb the band, the analysis has been made easy through the use of an elaborate set of asymmetric top computer programmes. The band centre and a set of upper state constants have been obtained. With these constants, 288 observed upper state energy levels have been fitted with a standard deviation of 0·021 cm^-1.

Using very simple expressions, we have predicted all the resonance effects perturbing the levels of ethylene near 2000 cm^-1. This led us to the identification of the v ₄ + v ₈ and v ₈ + v ₁₀ combination bands in low resolution spectra.     

High resolution Fourier transform infrared spectroscopy on CH2DI and CHD2I: evaluation of the ground state constants and analyses of the C-I stretching bands ν3

Abstract

The high resolution (0.0010cm^?1) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH₂DI and CHD₂1 have been recorded and analysed in the ν₃ band regions around 510cm^?1. The fundamental band ν₃ is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH₂DI and CHD₂I, respectively. About 4700 transitions in the case of CH₂DI and about 3900 transitions in the case of CHD₂I have been assigned. The ground state rotational constants of CH₂DI and CHD₂I have been obtained using the ground state combination differences calculated from the assigned ν₃ transitions and 16 microwave transitions from literature. The S reduced Watson's Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v₃=1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH₃I and CD₃I     

High-resolution infrared spectroscopy of CH281BrF near 8 μm: rovibrational analysis of the ν3 and ν8 fundamentals and resonances with the dark states 2ν5 and ν6 + ν9

The infrared spectrum of isotopically enriched CH₂⁸¹BrF was investigated in the ν₃ and ν₈ region between 1150 and 1370 cm^?1 at a resolution of 0.003 cm^?1. The ν₃ vibration of symmetry species A^′ gives rise to an a-/b-hybrid band with a-type predominance, while the ν₈ mode of A^″ symmetry produces c-type absorption. Due to the proximity of the band origins to those of closely lying overtones and combination bands, the v₃ = 1 and v₈ = 1 levels were found perturbed through Coriolis resonance by the v₅ = 2 (A^′) and v₆ = v₉ = 1 (A^″) states, respectively. The spectral analysis resulted in the identification of 3132 transitions (J^″ ≤ 98 and K_a^″ ≤ 14) for the ν₃ and 2958 transitions (J^″ ≤ 68 and K_a^″ ≤ 19) for the ν₈ bands. The assigned data were fitted using the Watson's A-reduction Hamiltonian in the I^r representation and the perturbation operators. Although no transitions belonging to the perturbers were observed, the band origins and excited state parameters for fundamentals and ‘dark states’ together with coupling terms for the ν₃/2ν₅ and ν₈/ν₆ + ν₉ dyads were determined.     

Infrared spectroscopy of van der Waals modes in the intermolecular potential of Ar-CO: The K a, = 0 combination of stretch and bending

Using our diode laser spectrometer a new subband of Ar^?CO in the 2167 cm^?1 region has been detected. We have assigned 18 rotational transitions to a thus far unobserved K _a = 0 van der Waals mode at 23.927cm^?1 above the ground state. An exact analysis yields a Coriolis coupling of this new observed state to a previously detected van der Waals state at 26.187cm^?1 [10]. The measurements and a complete analysis are presented.     

High resolution infrared synchrotron study of CH2D81Br: ground state constants and analysis of the ν5, ν6 and ν9 fundamentals

The high resolution infrared absorption spectrum of CH₂D⁸¹Br has been recorded by Fourier transform spectroscopy in the range 550–1075?cm^?1, with an unapodized resolution of 0.0025?cm^?1, employing a synchrotron radiation source. This spectral region is characterized by the ν₆ (593.872?cm^?1), ν₅ (768.710?cm^?1) and ν₉ (930.295?cm^?1) fundamental bands. The ground state constants up to sextic centrifugal distortion terms have been obtained for the first time by ground-state combination differences from the three bands and subsequently employed for the evaluation of the excited state parameters. Watson's A-reduced Hamiltonian in the I^r representation has been used in the calculations. The ν ₆?=?1 level is essentially free from perturbation whereas the ν ₅?=?1 and ν ₉?=?1 states are mutually interacting through a-type Coriolis coupling. Accurate spectroscopic parameters of the three excited vibrational states and a high-order coupling constant which takes into account the interaction between ν₅ and ν₉ have been determined.     

High resolution FTIR spectra and analysis of the ν11 fundamental and of the ν2 + ν11, ν5 + ν12 and ν7 + ν16 combination bands of 12C6D6

We report results from measurements of the high resolution FTIR spectrum for the fully deuterated benzene molecule C₆D₆ in the range 450–3500 cm^?1. Accurate spectroscopic constants have been obtained for the fundamental vibration ν₁₁ at 496.208 cm^?1 and improved ground state constants have been deduced from a fit of ground state combination differences. The J structure of the combination parallel bands ν₂ + ν₁₁ (at 2798.1 cm^?1), ν₅ + ν₁₂ (1802.5 cm_?1) and ν₇, + ν₁₆ (2619.3 cm^?1) of C₆D₆ has been analysed as well, from which improved values of the band origin and of the B and D _j constants of the excited states have been obtained. The strongest hot bands accompanying these parallel transitions have been assigned by means of the anharmonic force field calculated by Maslen et al. [1992, J. chem. Phys., 97, 4233]. In particular (ν₁₁ + ν₁₆) ? ν₁₆ is assigned to the band at 492.4 cm^?1 even though its shape is typical of a perpendicular transition (PAPE). New values for the ν₅, ν₁₂ and ν₁₆ band origins are determined from the band origins of combination bands and from calculated anharmonic constants. Numerous anharmonic constants are derived from the assignment of hot band and combination transitions.     

High-resolution Fourier-transform infrared spectroscopy of the ν1 and ν8 fundamental bands of sulphur tetrafluoride (SF4)

The vibration-rotation spectra of the ν₁ and ν₈ fundamental bands of ³²SF₄ have been observed using Fourier-transform infrared spectroscopy. The band centre of the c-type ν₁ symmetric sulphur-equatorial-fluorine stretching vibration was observed at 891.6 cm^?1 and that for the b-type ν₈ asymmetric sulphur-equatorial-fluorine stretching vibration at 864.6 cm^?1. In total, 2044 rovibrational transitions have been assigned. Analysis of the spectra showed that the rotational states of the ν₁ = 1 and ν₈ = 1 upper vibrational levels are coupled by an a-type Coriolis interaction. This coupling has been treated both using perturbation theory and by the explicit inclusion of an appropriate Hamiltonian matrix element in a combined fit of the data for both bands. Spectroscopic parameters have been determined for the ground, ν₁ = 1 and ν₈ = 1 vibrational levels. Weaker transitions resulting from difference bands and the fundamental bands of the ³⁴SF₄ isotopomer have been identified but could not be assigned, because of the density of lines in the room-temperature spectrum. The possibility that discrepancies between the observed and predicted spectra of the ν₁ fundamental may result from either a Coriolis interaction with the states of another vibrational level, or the effects of intramolecular exchange of axial and equatorial fluorine atoms is considered. The discussion is supported by theoretical calculations which show that the likely path for intramolecular exchange is via a C _4v transition state.     

The a-X electronic band system of selenium monoxide at 1.8 μm

The emission spectrum of the SeO molecule excited in a microwave discharge and recorded at low resolution revealed the existence of a brief band system in the near-infrared region 6470-5560 cm^?1. The system consists of five bands divided into two groups which were assigned as the Δv = 0 and +1 sequences of the transition a2-X₂1 (X being the case ?c³Σ^? ground state). An approximate value of the rotational constant B₀ of state a was obtained from the observed separation between the Q and R heads of the 0-0 band and the known value of B₀ of state X. The derived molecular parameters of state a are: ν₀₀ = 5566.2 cm^?1, $\text{Δ}\text{G(}\text{1}\text{2}\text{) = 833.3}\text{cm}{}^{\mathrm{?1}}$, B₀ = 0.45₆ cm^?1.     

High-resolution FTIR spectroscopy of the v11 and v2 + v7 bands of ethylene-d4

The Fourier transform infrared spectrum of the v₁₁ band of ethylene-d₄ (C₂D₄) has been recorded with an unapodized resolution of 0.006 cm^?1 in the frequency range 2150 to 2250cm^?1. The v₁₁ band, with a band centre of about 2201 cm^?1, was found to be perturbed by the nearby v₂ + v₇ band centred at about 2235 cm^?1 by a b-type Coriolis interaction. By fitting a total of 772 infrared transitions of v₁₁ using a Watson's A-reduced Hamiltonian in the I^r representation with the inclusion of b-type Coriolis interaction term, two sets of constants, up to quartic distortion constants for the v₁₁ = 1 state, and principal rotational constants for the v₂ + v₇ = 1 dark state, were derived. The inertia defect of the v₁₁ state was found to be 0.0693 ± 0.0004u Ų.     

The ν12 band of C2D4

The Fourier transform infrared (FTIR) absorption spectrum of the ν₁₂ fundamental band of ethylene-d₄ (C₂D₄) was recorded in the 1017-1137 cm⁻¹ region with an unapodized resolution of 0.0063 cm⁻¹. Upper state (v₁₂ = 1) rovibrational constants consisting of three rotational and five quartic constants were improved by assigning and fitting 2103 infrared transitions using Watson’s A-reduced Hamiltonian in the I^r representation. The band centre of the A-type ν₁₂ band is found to be 1076.98480 ± 0.00002 cm⁻¹. The present analysis covering a wider wavenumber range and higher J and K_c values yielded upper state constants including the band centre which are more accurate than previously reported. The rms deviation of the upper state fit is 0.00045 cm⁻¹. Improved ground state rovibrational constants were also determined from the fit of 1247 ground state combination differences (GSCD) from the presently-assigned infrared transitions of the ν₁₂ band of C₂D₄. The rms deviation of the GSCD fit is 0.00049 cm⁻¹. In the rovibrational analysis, local frequency perturbations were not detected even at high J and K_a values. The calculated inertial defect Δ₁₂ is 0.32551 ± 0.00001 μŲ. The line intensities of the individual transitions in the ν₁₂ band were measured and the band strength of 39.8 ± 2.0 cm⁻² atm⁻¹ was derived for the ν₁₂ band of C₂D₄.     

Ultraviolet laser-induced fluorescence spectrum of fluorochlorocarbene in solid argon

CFCl has been produced for spectral investigation by matrix reactions of alkali metal atomic beams with CFCl₃ in argon followed by rapid quenching to 15°K on a tilted copper wedge. When these samples were irradiated with near uv light from a krypton ion laser, a very intense, highly structured fluorescence spectrum was observed. This emission system extended from about 25 000 cm^?1 to 15 000 cm^?1 and peaked in intensity at about 22 000 cm^?1. The three most intense progressions are assigned to transitions from a common excited state to ground state levels (0v₂0), (1v₂0) and (1v₂1). New molecular constants determined from these progressions include $\text{ω}{}_2{}^0\text{= 446}\text{cm}{}^{\mathrm{?1}}$, x₂₂ = ?1.2 cm^?1, x₁₂ = ?3 cm^?1, x₂₃ = ?4 cm^?1, and x₁₃ = ?6 cm^?1. CFCl was also produced by in situ photolysis of CFCl₃ using laser plasma emission and by alkali metal atom reactions with CF₂Cl₂, CF₂ClBr, and CHFCl₂.