Microwave spectrum of methylene fluoride in excited vibrational states

The rotational spectra of ¹²CH₂F₂ in seven of the nine fundamental vibrational states and also in overtone and combination states involving the ν₄ mode were observed and assigned. Coriolis interactions between ν₃ and ν₇, ν₂ and ν₈, ν₃ and ν₉, and ν₅ and ν₇ were analyzed by using approximate expressions for the rotational levels. An effective Hamiltonian with the Coriolis term in the off-diagonal block was applied to stronger interaction between ν₃ and ν₉. Fermi resonance between ν₃ and 2ν₄ was found to be negligible. The ground state spectra of ¹²CH₂F₂ and of ¹³CH₂F₂ were remeasured to improve the accuracy of the rotational and centrifugal distortion constants. The Coriolis coupling constants and the energy differences between two vibrational levels in resonance, which were obtained through an analysis of the satellite spectra, are compared with the results derived from a normal coordinate analysis.     

Analysis of Coriolis perturbations in the high-resolution infrared spectra of arsine (AsH3)

Numerical methods for the analysis of high-resolution infrared spectra of symmetric top molecules perturbed by Coriolis interactions between degenerate and nondegenerate vibrational levels are discussed in the second order of approximation. Application to the high-resolution infrared spectra of the AsH₃ molecule in the region of the fundamentals ν₁, ν₃ and ν₂, ν₄ yields considerably improved values of the molecular constants of AsH₃, including the band origins rotational constants, Coriolis coupling constants, centrifugal distortion constants, and the parameter of the K-type doubling effect.     

Fourier transform infrared spectra of H2CS and D2CS

Infrared spectra of thoformaldehyde, H₂CS and D₂CS, were observed in the gas phase at a resolution of better than 0.1 cm^?1 from 4000 to 400 cm^?1 using a Nicolet FTIR system. Vibrational band origins and rotational constants were determined for ν₂, ν₃, ν₄, and ν₆ of H₂CS and for ν₁, ν₂, ν₃, ν₄, and ν₆ of D₂CS. The ν₃, ν₄, and ν₆ bands of H₂CS were analyzed as a set of three Coriolis interacting bands, and three Coriolis constants were determined; similarly the ν₄ and ν₆ bands of D₂CS were analyzed as a pair of interacting bands and one Coriolis constant was determined. A general harmonic force field was determined, without constraints, to fit the vibrational wavenumbers, Coriolis constants, and centrifugal distortion constants. A zero-point (r_z) structure was determined from the ground-state rotational constants, and the equilibrium (r_e) bond lengths were estimated.     

Microwave spectrum of formic acid and its isotopic species in D, 13C and 18O. Study of Coriolis resonances between ν7 and ν9 vibrational excited states

In the investigation of the 8 → 280 GHz region, 241 and 57 transitions of H¹²COOH and DCOOH, respectively, have been assigned to the ν₇ and ν₉ vibrational states coupled by a strong Coriolis resonance. The numerical analysis based on Watson's theory of centrifugal distortion coupled with the addition of Coriolis interaction allows us to obtain a set of parameters which fits the transitions well. The rotational spectra of the isotopic species HCOOD and DCOOD have also been investigated. In this investigation 55 and 67 transitions have been assigned to the ν₇ and ν₉ vibrational states of these two molecules, respectively. A very weak Coriolis resonance was detected. Two non-rigid independent rotors were thus employed and gave us a set of parameters which fits the transitions quite well. The rotational spectrum of the ground state of H¹²COOH, H¹³COOH, HCOOD, DCOOH, H¹²C¹⁶O¹⁸OH, and H¹²C¹⁸O¹⁶OH have been reinvestigated and a set of improved parameters was obtained for each species.     

Infrared diode laser spectroscopy of FCO: The ν1 and ν2 bands

The ν₁ (CO stretching) and ν₂ (CF stretching) bands of the FCO radical were observed with Doppler-limited resolution by an infrared diode laser spectrometer with Zeeman and source modulation. The FCO radical was generated by a 60-Hz discharge in one of the following three gas mixtures: O₂ + C₂F₄, CO + SF₆, and CO + C₂F₄, all diluted with He. The observed spectra were analyzed to determine the rotational constants, the centrifugal distortion constants, and the spin-rotation interaction constants. The band origins, 1861.6372(1) and 1026.1283(1) cm^?1 [with standard errors in parentheses], which were obtained, were found to agree well with matrix data, 1857 and 1023 cm^?1, respectively. The assignment of the observed spectra to the FCO radical was further supported by observing the ν₁ band of F¹³CO, which was obtained from ¹³CO and SF₆. The molecular structure and the force field of FCO are briefly discussed by using molecular constants obtained from the observed spectra.     

Millimeter- and Submillimeter-Wave Spectra of CD2F2

The millimeter- and submillimeter-wave spectrum of ¹³CD₂F₂ present in natural abundance in methylene fluoride-d₂ (CD₂F₂) has been measured in the region 230-380 GHz. The spectrum was recorded using a frequency-modulated millimeter- and submillimeter-wave spectrometer. More than 200 rotational transitions in the ground state of ¹³CD₂F₂ with J≤45 and K_a≤8 have been assigned. A combined weighted least squares fit of the newly assigned transitions with previously reported microwave data has been carried out in the Watson's A- and S-reduced Hamiltonian. The data have been fitted with a standard deviation approaching the experimental accuracy, to provide improved values for the rotational and quartic centrifugal distortion constants, including sextic distortion constants for the ground state of ¹³CD₂F₂.     

ν7 and ν9 bands of formic acid near 16 μm

The ν₇ and ν₉ fundamental bands of formic acid were studied by Fourier transform spectroscopy with a resolving power of 0.020 cm^?1. Band centers obtained are ν₇ = 626.158 cm^?1 and ν₉ = 640.722 cm^?1. It was possible to determine rotational and centrifugal distortion parameters for both vibrational states v₇ = 1 and v₉ = 1 and also the two first-order Coriolis interaction parameters along z and x axes and the second-order Coriolis parameter along z axis. The stability of rotational and distortion parameters compared to ground state values confirms that a Watson type Hamiltonian is well adapted to such a problem.     

The rotational a-type sepctra of 15N-labeled diazirine,H2CN2

The rotational a-type spectra of isotopically enriched diazirine isotopomers, H₂¹²C¹⁴N¹⁵N and H₂¹²C¹⁵N₂, have been recorded in the region between 8 and 300 GHZ; the latter isotopomer has been observed for the first time. Using Watson's A-reduced Hamiltonian, the rotational constants and the quartic and some sextic centrifugal distortion constants have been determined for the ground vibrational states.     

Rotational and hyperfine constants of CD3I

The rotational spectra of CD₃I (v = 0; v₃ = 1; v₆ = 1) and of ¹³CD₃I in its ground state were observed between 8 and 320 GHz. For the ground state of CD₃I, pure quadrupole resonances were also measured by laser-radiofrequency double resonance. These data have been used to determine with high accuracy the rotational, centrifugal distortion, and hyperfine constants.     

High resolution infrared spectrum of the ν2 + ν3 and ν1 + ν2 bands of ozone

The vibration-rotation bands ν₁ + ν₂ and ν₂ + ν₃ of ozone appearing in the 5.7 μm region have been recorded at a resolution of 0.019 cm^?1 with a SISAM spectrometer. The rotational levels of the (110) and (011) vibrational states have been fitted using a Hamiltonian which takes into account the Coriolis interaction between these two states. The rotational and coupling constants deduced from this study have been used to calculate a list of the vibration-rotation lines which is of interest for high resolution studies of atmospheric spectra in the 1670–1890 cm^?1 region.     

The rotational spectra of the 79, 69, and 7 vibrational states of nitric acid

The rotational spectra of the first three vibrational states of nitric acid above 1000 cm⁻¹, 7¹9¹, 6¹9¹, and 7², have been measured and analyzed. The 7² state, along with the previously published 7¹ state, show the rotational and centrifugal distortional constants have a near linear dependence on the υ₇ vibrational quantum number. Large changes for several centrifugal distortion constants of the υ₇ = n series of states are attributed to a c-type Coriolis resonance manifold between the ν₇ and ν₆ vibrational modes and the Hamiltonian reduction and representation used to fit the spectra. The 7¹9¹ and 6¹9¹ states have torsional splittings of 12.361(8) and 22.47(1) MHz, respectively. These splittings are large compared to 2.340(8) MHz of the 9¹ state and can be explained by a ∼1-2% mixing through anharmonic Fermi resonances with the 9³ state, which has a large torsional splitting of ∼1760 MHz. The millimeter/submillimeter-wave spectrum of each state was fit separately to the experimental uncertainty of the measurements. The resultant rotational constants, distortional constants and inertial defects agree well with DFT calculations.     

Spectroscopic constants of the ground and lower vibrational states of CH2BrF: A combined high resolution infrared and microwave study

The enriched ⁸¹Br isotopic species of bromofluoromethane has been investigated in the infrared and microwave regions. The rovibrational spectrum of the ν₅ fundamental has been studied by high resolution FTIR spectroscopy, while the rotational spectra of the ground and v₆ = 1 states have been observed by means of microwave spectroscopy. More than 2700 transitions have been assigned in the ν₅ band and the analysis of the rovibrational structure reveals a first-order c-type Coriolis resonance with the v₆ = 2 state. The present study improves the ground state constants available in the literature and enables the determination of further centrifugal distortion parameters together with the full bromine quadrupole coupling tensor. A set of spectroscopic parameters up to the sextic distortion terms for the vibrational excited states has been accurately evaluated for the first time.     

High-resolution infrared spectrum of the ν2 and ν8 bands of CH2D2

A high-resolution infrared spectrum of methane-d₂ has been measured in the C-D stretching band region (2025–2435 cm^?1). Rotational structures of the ν₂ and ν₈ bands have been assigned by use of the ASSIGN-diagram method, and the c-type Coriolis interaction between ν₂ and ν₈ has been analyzed. The band origins, ν₂ = 2203.22 ± 0.01 cm^?1 and ν₈ = 2234.70 ± 0.01 cm^?1, the rotational constants and the centrifugal distortion constants for the two bands, and the Coriolis coupling constant, $\text{∥;ξ}{}_{28}{}^{\mathrm{c}}\text{∥; = 0.182 ± 0.015}\text{cm}{}^{\mathrm{?1}}$, have been determined.     

Vibration-rotation spectra and molecular force field of methylene fluoride and methylene fluoride-d2

Infrared spectra of CH₂F₂ and CD₂F₂ have been measured under a medium resolution. The vibration-rotation bands of CD₂F₂ fundamentals have been analyzed and the assignment for the fundamentals of CD₂F₂ is given. In addition, a number of overtone and combination bands are observed for CH₂F₂, which helps to clarify the vibrational assignment for CH₂F₂. A normal coordinate treatment has been carried out: The force constants in a modified Urey-Bradley as well as the general valence force fields have been determined, the vibrational frequencies and the centrifugal distortion constants obtained from microwave spectroscopy being used. The force constants of the methylene fluoride molecule are discussed in connection with those of the related molecules. Special features of the CH₂F₂ and CD₂F₂ spectra are also described.     

Centrifugal distortion and internal rotation analysis of the rotational spectra of N-methylmethanimine d0 and d5

The ground state millimeter-wave spectra of CH₃NCH₂ and CD₃NCD₂ have been measured. The rotational constants, centrifugal distortion constants, and barrier hindering internal rotation of the methyl group have been determined for both species. For the parent species I_α and ?(i,a) were also obtained, and for the perdeuteriated species the quadrupole coupling constants of ¹⁴N were determined.     

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 potential function and rotation-vibration energy levels of the methyl radical CH3

The equilibrium bond length and the shape of the complete potential energy curve for the methyl radical CH₃ are determined. This is done by fitting the experimental data [mainly from C. Yamada, E. Hirota, and K. Kawaguchi, J. Chem. Phys.75, 5256–5264 (1981)] using the nonrigid invertor Hamiltonian and a model anharmonic potential function. As a result the v₂ (out-of-plane bending) dependence of the rotational constants is explained and the v₂ dependence of the spin-rotation coupling constants is modeled. In addition, some of the vibrational energies and rotational, centrifugal distortion, and spin-rotation constants are predicted for the ¹³CH₃, ¹²CD₃, and ¹²CT₃ isotopes.     

Vibration-rotation spectra of CD3CCH

Rotational structure in the perpendicular fundamentals ν₆, ν₇, and ν₈, and in the parallel component of 2ν₉ of CD₃CCH are fully analyzed at a resolution of 0.2–0.3 cm^?1. The A₁-E Coriolis resonances between ν₄ and ν₇, and ν₅ and ν₈ are analyzed by computer contour simulations. These permit accurate location of the parallel fundamentals, and determination of the associated Coriolis interaction constants. The fundamental vibrations ν₅ and ν₈ in CD₃CCH lie only 4 cm^?1 apart, and constitute the closest accidental Coriolis resonance yet studied by the simulation technique. The force field of methyl acetylene, constrained according to the hybrid orbital model, is calculated, using the recently determined molecular structure, and fitting all observed data, many of which have been revised in a number of recent studies.     

Diode laser spectrum and analysis of the 882-cm−1 band of s-tetrazine

A high-resolution diode laser spectrum of the 882-cm^?1 band of s-tetrazine has been obtained. A complete rotational analysis of this band, incorporating quartic and sextic centrifugal distortion coefficients, has been carried out. The rotational constants A, B, and C have been determined with an accuracy better than 10^?5 cm^?1. The analysis has shown the band to be A-type and, on this basis, the vibrational assignment of this band has been revised from ν₁₂ to ν₁₄.     

Microwave spectrum of silyl fluoride: Coriolis resonance between ν2 and ν5 states

The J = 1 ← 0 and J = 2 ← 1 microwave rotational transitions of SiH₃F and SiD₃F have been measured for the ground and the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 vibrational states, for which the various rotational and vibration-rotation interaction constants have been obtained. Both molecules show an X-Y Coriolis resonance between the ν₂ and ν₅ vibrational states, whose separation are 29 and 8 cm^?1, respectively. In the case of SiD₃F the resonance is very strong and an exact numerical diagonalization of the energy matrix was employed.