Ν8 State Research Articles

Unraveling torsional bath interactions with the CO stretching state in methanol

Quantum mechanical models describing the effects of a C3 internal rotor have been successful in modeling all the torsional manifolds of isolated vibrational states. However, modeling the coupling between nearly degenerate small amplitude vibrations in the C3 internal rotation case remains far from satisfactory and a variety of practical and fundamental questions persist on basis sets, the relative importance of effects and how the problem should be approached. The ν8 C–O stretching state of methanol has been well studied with infrared techniques and has the potential to serve as an experimental reference data set for the development of models for the coupled large and small amplitude motion case. A combined infrared-microwave study of the lowest K A-states of vt=3, vt=4 and ν8 has been performed to understand the nature of the interactions between ν8 the excited torsional states. The interaction between vt=4 and ν8 at K=0+ has been confirmed to be Fermi type with magnitude of 2.5cm−1. Additionally, the fundamental a-symmetry and b-symmetry Coriolis interactions between vt=3 and ν8 have been estimated to be 8900MHz and −360MHz, respectively. The magnitude of these interactions suggests that modeling the ν8 state, the vt=3 state, and the vt=4 states will have to carefully account for these interactions.

High-Resolution Infrared Study of Vinyl Fluoride in the 750−1050 cm-1 Region: Rovibrational Analysis and Resonances Involving the ν8, ν10, and ν11 Fundamentals

The FTIR spectra of CH2[double bond]CHF have been investigated in the nu(8), nu(10), and nu(11) region between 750 and 1050 cm(-1) at a resolution of about 0.002 cm(-1). The nu(8) vibration of symmetry species A' gives rise to an a/b-type hybrid band, while the nu(10) and nu(11) modes of A' ' symmetry produce c-type absorptions. Due to the proximity of their band origins, the three vibrations perturb each other by Coriolis and high-order anharmonic resonances. In particular, the interactions between the nu(8) and nu(10) modes are very strong and widespread with band origins separated by only 1.37 cm(-1). Besides the expected c-type characteristics, the nu(10) band shows a very intense pseudo a-type component caused by the strong first-order Coriolis resonances with the nu(8) state. Furthermore, the 2nu(9) "dark state" was found to be involved in the interacting band systems. The spectral analysis resulted in the identification of 3144, 3235, and 3577 transitions of the nu(8), nu(10), and nu(11) vibrations, respectively. Almost all the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the Ir representation and the perturbation operators. The model employed includes nine types of resonances within the tetrad nu(8)/nu(10)/nu(11)/2nu(9) and a set of spectroscopic constants for the nu(8), nu(10), and nu(11) fundamentals as well as parameters for the "dark state" 2nu(9), and fourteen coupling terms have been determined.

Microwave, Submillimeter-Wave, and High-Resolution FTIR Study of SO2F2 in the ν8 State

The high-resolution infrared spectrum of the ν8 band of SO2F2 (νas SF2) centered at 887.2 cm−1 has been recorded with a resolution of 2.4 × 10−3 cm−1. More than 8000 transitions of the C-type band with ΔKa = ±1 (and in addition some ΔKa = ±3 transitions) have been assigned. Microwave and millimeter-wave spectra of the v8 = 1 state up to 450 GHz have been recorded, and 177 pure rotational transitions have been measured. Rotational and rovibrational data have been combined, and excited state parameters up to sextic centrifugal distortion constants have been determined using a Watson-type Hamiltonian in S-reduction. No perturbation was indicated.

High-resolution FTIR study of the ν2 band of CH2F2 and Coriolis interaction between the ν2 and ν8 states

The very weak ν2 (1509.15cm−1) band of the CH2F2 molecule has been observed for the first time in infrared. The high-resolution (0.002cm−1) FTIR absorption data of this band have been analyzed by taking into account the Coriolis interaction with the ν8 (1435.63cm−1) state. A strong intensity perturbation was observed which enhances the intensity of the ν2 band. More than 1500 (J≤57 and Ka≤21) transitions were assigned in the ν2 band, and a simultaneous weighted least-squares fit of the data of the ν2 and ν8 bands was carried out including microwave data. The molecular parameters and Coriolis interaction parameters obtained from the fit satisfactorily reproduce the observed relative intensity of the spectrum. By simulating the spectrum, positive perturbation has been confirmed.

ChemInform Abstract: The High‐Resolution Mid‐Infrared FT Spectrum of Difluorodioxirane CF2O2: The Ground, ν1, ν2, and ν8 States.

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The High-Resolution Mid-infrared FT Spectrum of Difluorodioxirane CF2O2: The Ground, ν1, ν2 and ν8 States

The infrared spectrum of CF2O2 has been studied in the 800-1600 cm−1 region with a resolution of ca. 0.003 cm−1. Rotational fine structure was resolved, and the supposed cyclic difluorodioxirane structure with C2v symmetry, κ = −0.0632, was confirmed. The ν1 and ν2 bands, which reveal a-type structure and are centered at 1466.591 and 917.905 cm−1, respectively, and the c-type band ν8 centered at 1062.102 cm−1 have been analyzed employing Watson′s A-reduced Hamiltonian in the Ir representation. For each of these bands, between 4100 and 5600 lines were fitted, with σ = 3.5-4 × 10−4 cm−1. No perturbations were found. Ground state constants of the novel CF2O2 molecule were determined for the first time from a fit of ca. 7500 ground state combination differences formed from transitions belonging to ν1, ν2, and ν8, which were fitted with σ = 4 × 10−4 cm−1. The rotational constants A0 = 0.26575541(28) cm−1, B0 = 0.21095653(14) cm−1, and C0 = 0.16266791(15) cm−1 were determined. Assuming a CF bond length of 131.5 pm, the structural parameters d(CO) = 134.9 pm, d(OO) = 157.6 pm, and ∠ (FCF) 109.05° were derived.

X–y Coriolis interaction in the ν5 and ν8 bands of propyne-d3

High resolution Fourier transform spectra of the ν5 and ν8 bands of CD3C≡CH have been recorded and analyzed taking into account the strong x–y Coriolis interaction between these fundamentals. Fermi resonance of the ν8 state with the ν9 + ν10 state, l-type doubling interaction between the ± l components of ν8 and a weak k-type doubling interaction between the ν5 and ν8 states have also been included in the perturbation treatment. The parameters of the ν5 and ν8 states as well as some of the parameters of the unobserved ν9 + ν10 state have been determined. An estimate of the relative value of the transition moments has been obtained from the line intensities, which are strongly affected by the x–y Coriolis interaction.

High-Resolution Infrared Spectroscopy of the ν4 + ν8 − ν8 Band of CH3NC

The vibration-rotation spectrum of the ν4 + ν8 − ν8 band for CH3NC has been observed and measured with an interferometric spectrometer with a spectral resolution of 0.004 cm−1; 175 transitions were assigned to the P( J, k, l) branches spanning J = 5-29 and k = 3-8. Spectroscopic constants for the ν4 + ν8 state were obtained through a least-squares fit by explicitly taking account of the l-resonance. The validity of the additivity rule of molecular constants is discussed. Small anomalies detected in the K = 3 and 4 subbands of the ν4 + ν8 − ν8 band were ascribed to a rotational resonance (Δl = ∓1, Δk = ±2) between the ν4 + ν8 and 4ν−28 states.

Ethylene hot bands from molecular jet double-resonance spectroscopy

Part of the ν10 + ν9 ← ν10 hot-band spectrum, as well as a few lines of the ν7 + ν9 ← ν7 hot band of ethylene, C2H4, have been recorded in a free molecular jet using a double-resonance technique. The identification of the hot-band transitions starting from ν7 has been confirmed in a separate experiment on a (collision-free) molecular beam. Experimentally determined wave-numbers and intensities are given for 169 hot-band lines, 124 of which have been identified. Additional information on symmetry species and rotational energy of the lower levels of a number of as yet unidentified hot-band lines has been obtained from their relaxation behavior. The double-resonance spectra have been confirmed and completed at higher J and Ka values by spectra recorded with a difference frequency spectrometer. The analysis of the ν9 + ν10 state, based on 153 experimentally determined levels, takes into account b-type Coriolis interactions with ν7 + ν11 and ν1 + ν8 states and an anharmonic resonance with the 2ν4 + 2ν8 state, yielding a 0.003 cm−1 standard deviation.

ChemInform Abstract: Microwave Spectrum of Diacetylene‐d in the Ground and Excited Vibrational States.

Abstract Rotational spectra of diacetylene-d (DCCCCH), which is nonpolar in the equilibrium configuration, were observed with a source-modulated microwave spectrometer. Rotational transitions in the ground, ν8, and ν9 vibrational states were newly identified, where ν8 and ν9 denote the ∠CCD bending and lowest skeletal bending modes, respectively. Small dipole moments, 0.0115 ± 0.0012 D for the ground state and 0.030 ± 0.008 D for the ν8 state, were obtained from the intensity measurement. The rotational and centrifugal distortion constants for the ground state are 4084.4546 ± 0.0018 MHz and 0.402 ± 0.012 kHz, respectively, where the uncertainties correspond to 3σ.

Microwave spectrum of diacetylene-d in the ground and excited vibrational states

Abstract Rotational spectra of diacetylene-d (DCCCCH), which is nonpolar in the equilibrium configuration, were observed with a source-modulated microwave spectrometer. Rotational transitions in the ground, ν8, and ν9 vibrational states were newly identified, where ν8 and ν9 denote the ∠CCD bending and lowest skeletal bending modes, respectively. Small dipole moments, 0.0115 ± 0.0012 D for the ground state and 0.030 ± 0.008 D for the ν8 state, were obtained from the intensity measurement. The rotational and centrifugal distortion constants for the ground state are 4084.4546 ± 0.0018 MHz and 0.402 ± 0.012 kHz, respectively, where the uncertainties correspond to 3σ.

Diode Laser Spectrum of the ν8 Band of CH3SH

Abstract The Stark effect was used to assign four series of the transitions in the heavily perturbed spectrum of methanethiol in the 14 μm region: K=0 and two K=1 series of A torsional symmetry and K=0 series of E symmetry. Effective parameters were determined for each series. The K=0 levels of A symmetry in the ν8 state were found to be perturbed by a Fermi-type resonance.

Microwave spectra of CH 314NC and CH 315NC in the 4 ν8 state

The J → J + 1 transitions ( J = 4, 5, 6, 7, 8) in the microwave spectra of methyl isocyanide and its 15N derivative have been obtained and analyzed in the 4 ν 8 degenerate vibrational state. Theoretical analytical expressions are given for the rotational frequencies in a 4 ν E state, separately for the l = 0, ±2, ±4 values. These formulas could only be used as a starting point for the assignment and analysis, because of the complexity of the spectrum and the number of accidental resonances appearing in many l = 0 and ±2 lines for low K values. A detailed analysis was obtained through a diagonalization of the energy matrix. Many types of A 1 A 2 doublings could be localized; in particular for CH 3 15NC the K, l = ±1, ±4 doubling allowed the calculation of the g 6 coefficient of the 〈 K, l| H|, l ± 6〉 term. As in the 3 ν 8 state, some lines seem to undergo the effects of a vibrational resonance. A set of constants is given for both species, and a comparison is made with the other states.