Microwave spectrum of trans 3-fluorophenol in excited torsional states

The microwave rotational spectra of the trans conformer of 3-fluorophenol have been observed in excited torsional states and analyzed in the frequency range 12.0-43.0 GHz using conventional microwave and Radio-Frequency Microwave Double Resonance (RFMWDR) techniques. Analysis of the ground torsional state spectrum has been extended to higher rotational states. Least-squares analysis of three sets of rotational transitions yield rotational and centrifugal distortion constants for the ground and first two excited torsional states. A nonlinear behavior of the variation of inertial defect with the torsional quantum number was observed.     

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.     

Millimeter wave spectrum of glycine

We present new investigations of the millimeter wave spectra of the two lowest-energy conformers of glycine (NH₂CH₂COOH). Measurements of these spectra have been carried out between 75 and 260 GHz using the millimeter-wave spectrometer in Kharkov. The new data set involves rotational transitions with J up to 44 and K_a up to 15 for conformer I and transitions with J up to 43 and K_a up to 14 for conformer II. This represents a more than twofold expansion both in the frequency range and J quantum-number range in comparison with previous investigations. The improved sets of spectroscopic parameters obtained for both conformers provide accurate transition frequencies for the key lines necessary for radio astronomy searches for interstellar glycine.     

The structure and helicity of perfluorooctanonitrile, CF3–(CF2)6–CN

New molecular structural data is presented for a cyanide terminated oligomer of polytetrafluoroethene. The target molecule, CF₃–(CF₂)₆–CN, has been seeded within a pulsed supersonic expansion of argon. The result of this action is to cool the species to rotational temperatures below 4 K. Within this state, the pure rotational spectrum of the oligomer has been recorded using two types of Fourier transform microwave spectroscopy. A total of 111 transitions have been identified involving rotational J levels between 6 and 40. Only a- and b-type transitions were observed. The spectrum has been analyzed using a Hamiltonian containing all three rotational constants and one centrifugal distortion constant, D_J. The experimental spectroscopic constants have been used to develop an effective molecular structure by scaling the quantum chemical calculated structure. The data shows that the seven carbon perfluorinated chain for the isolated oligomer twists ≈104°. This compares well to the C₇F₁₃-twist of ≈97° anticipated from the X-ray structure of phase II polytetrafluoroethene.     

Far-infrared spectrum and ground state constants of methyl amine

The far-infrared spectrum of methyl amine has been studied in the region 40 to 350 cm⁻¹ by Fourier transform spectroscopy with an apodized resolution of 0.005 cm⁻¹ or better. Both the pure rotational spectrum and the spectrum of the fundamental torsional band have been assigned. This paper reports the ground state constants obtained from a global fitting of a data set including ground state microwave transitions from the literature, as well as far-infrared pure rotational ground state transitions and ground state combination differences from the torsional band obtained in this work. Slightly over 1000 energy differences for the ground state with 0 ≦ K ≦ 19 and K ≦ J ≦ 30 were fit to 30 molecular parameters from a group theoretical formalism developed earlier, and a standard deviation of ±0.00063 cm⁻¹ was obtained. An ambiguity (noted earlier in the microwave literature) in the determination of the structural parameter ϱ, which arises when two large amplitude motions are present in the molecule, can be understood and resolved using the present formalism.     

The far-infrared spectrum of fluoroform (CHF3)

The far-infrared spectrum of fluoroform has been recorded in the region between 7 and 60 cm⁻¹ at a resolution of 0.002 cm⁻¹. More than 1400 rotational transitions in the ground state have been measured and assigned up to J″ = 80. Simultaneous analyses of these measurements and of microwave and millimeter-wave data reported previously have been performed. Improved values of the ground state rotational and centrifugal distortion constants, including the sextic distortion constants reported for the first time, have been obtained. Rotational transitions in a few low-lying vibrational states have also been observed.     

A new joint analysis of the ground and first excited torsional states of methylformate

A global fit within experimental accuracy of microwave rotational transitions in the ground and first excited torsional states (v_t = 0 and 1) of methylformate (HCOOCH₃) is reported, which combines older measurements from the literature with new measurements from Kharkov. In this study the so-called ‘‘rho axis method’’ that treats simultaneously both A and E species of the ground and first excited torsional states is used. The final fit requires 55 parameters to achieve an overall unitless weighted standard deviation of 0.71 for a total of 10533 transitions (corresponding to 9298 measured lines) with rotational quantum numbers up to J ? 62 and K_a ? 26 in the ground state and J ? 35 and K_a ? 23 in the first excited torsional state. These results represent a significant improvement over past fitting attempts, providing for the first time a fit within experimental accuracy of both ground and first excited torsional states.     

Microwave fourier transform spectroscopy of pure rotational ν4 ↔ ν4 transitions and reanalysis of the ν2ν4 dyad of methane-d4

Pure rotational transitions of a spherical top in a degenerate vibrational state have been observed directly for the first time with the help of pulsed microwave Fourier transform (MWFT) spectroscopy. Twelve rotational transitions in the v₄ = 1 vibrational excited state of CD₄ have been identified. The theoretical basis for the transition moments has been developed and the line strengths of the rotational transitions have been estimated. The measured rotational transition frequencies have been included in a reanalysis of the data from a previously recorded high-resolution FTIR spectrum of the ν₂ and ν₄ bands. The v₄ = 1 state of CD₄ is strongly coupled to the v₂ = 1 state by Coriolis interaction. Thirty molecular parameters of the $\text{ν}{}_2\text{ν}{}_4$ dyad have been fitted finally from the combined microwave and infrared data. The microwave data are reproduced with a standard deviation of 42 kHz, and the infrared data with a standard deviation of 0.0002 cm^?1; in each case, this is close to the estimated experimental prescision.     

Microwave spectra and structure of the fluorobenzene-carbon monoxide van der Waals complex

The rotational spectra of the fluorobenzene–CO complex and four of its isotopomers have been measured between 5–18GHz with a pulsed nozzle Fourier transform microwave spectrometer. An analysis with a rigid asymmetric rotor model revealed that CO must be located above the ring plane with CO at an angle to the symmetry plane. A second set of transitions indicated that CO is executing large amplitude motions. The rotational transitions of two states were analysed simultaneously using an effective model Hamiltonian which accounts for an internal rotation between CO and fluorobenzene hindered by a low barrier (below 25cm^-1).     

Centrifugal distortion analysis of difluoramine

The microwave rotational spectrum of difluoramine (NF₂H) has been analyzed in the frequency region 15–36 GHz involving rotational levels up to J = 19. The analysis gives refined rotational constants and all quartic centrifugal distortion constants. These constants have been used to predict additional Q-branch transitions of the molecule in the frequency region 5–95 GHz.     

Microwave and submillimeterwave spectra of CH2DI and CHD2I

The pure rotational spectra of CH₂DI and CHD₂I have been measured by microwave Fourier transform spectroscopy, millimeterwave spectroscopy and submillimeterwave spectroscopy. The quadrupole hyperfine structure due to iodine has been analyzed by direct diagonalization of the quadrupole tensor. For the J = 1-0 transition of the ground state of CH₂DI, the quadrupole hyperfine structure due to deuterium could be resolved and the quadrupole coupling constant eQq_aa(D) determined.Accurate rotational and centrifugal distortion constants (up to sextic terms) have been determined. They are compared to the constants derived from the ground state combination differences (GSCD). A good agreement is observed but it is also found that the two kinds of data (GSCD and microwave) are complementary and a combined fit allows us to significantly improve the accuracy of the constants.     

The eight first vibrational states of the water molecule: measurements and analysis

In this work the spectrum of the water molecule has been the subject of extensive experimental and theoretical investigations. More than 1500 transitions have been assigned in a far infrared emission spectrum recorded in the 50-500 cm⁻¹ region and experimental rotational energies have been obtained for the second triad of interacting states, (0 3 0), (1 1 0), and (0 1 1), up to J=10 using flame spectroscopy. These new data along with a large data set of already published experimental rotational energies, high-resolution infrared transitions, and microwave lines, involving the eight first vibrational states, have been analyzed using the theoretical formalism developed for water in a previous paper (J. Mol. Spectrosc. 206 (2001) 83), which accounts for the anomalous centrifugal distortion as well as for the Fermi- and Coriolis-type couplings.     

Microwave spectroscopy of propynal in the v2 = 1 vibrational state by IR-MW triple resonance

Infrared-microwave triple resonance was applied to microwave spectroscopy of propynal, HCCCHO, in the v₂ = 1 vibrational state. Eleven microwave transitions were newly observed by using a Zeeman-tuned 3.51 μm HeXe laser as the infrared radiation source. The spectrum was analyzed including the 11 transitions previously observed by double resonance. A least-squares fit of the 13 low-J transitions revealed that the rotational constants in the K_?1 = 1 states were slightly different from those of the K_?1 = 0 states. A higher-order rotational resonance was proposed for explanation of the effect.     

Microwave spectrum,conformation, and dipole moment of 4-thiacyclohexanone

The microwave spectra of 4-thiacyclohexanone in the ground state and eight vibrationally excited states have been studied in the frequency region 18.0–40.0 GHz and the corresponding rotational constants have been determined. The following values of the ground-state rotational constants (MHz) were obtained from the analysis of the a-type transitions: A = 3935.149 (0.031), B = 1829.444 (0.001), and C = 1364.609 (0.001). Analysis of the Stark effect gives for the dipole components (in Debye units) μ_a = 1.409 (0.002), μ_c = 0.391 (0.064). These data are consistent with a chair conformation for the ring. A phisically reasonable set of structural parameters which reproduce the ground-state rotational constants has been derived. A qualitative estimate of the low-frequency vibrational modes was obtained from relative-intensity measurements. The lowest vibrational frequency is believed to be a ring-bending mode and it occurs at 77 ± 22 cm^?1 while the ring-twisting mode is at 204 ± 27 cm^?1.     

Two conformers of ethyl pivalate studied by microwave spectroscopy

The rotational spectra of two conformers of ethyl pivalate, (CH₃)₃C-COO-C₂H₅ have been recorded by molecular beam FT microwave spectroscopy. The analysis yielded a set of three rotational constants and five quartic centrifugal distortion constants for each conformer. The conformers were identified by comparing the experimental rotational constants with those obtained by ab initio calculations at MP2/6-311++G∗∗ level. One conformer has C_s symmetry, the other one forms a pair of enantiomers with C₁ symmetry. Additionally, the torsional potentials of the tert-butyl group and of the methyl groups were obtained by ab initio methods.     

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.     

The microwave spectrum and centrifugal distortion constants of propiolic acid

The microwave spectra of propiolic acid and propiolic acid-d have been measured up to J = 30. These have enabled accurate evaluation of the rotational and centrifugal distortion constants for each species. The measured frequencies are presented, along with some predictions of transitions unmeasured in the present work, but of potential use in radioastronomy.     

Submillimeter-wave spectrum of the FCO radical

The submillimeter-wave spectrum of FCO has been measured using a backward-wave oscillator based spectrometer in conjunction with a free space absorption cell. The FCO radical has been produced in glow discharge plasma of a gaseous mixture of F₂CO, Ar, and He. A total of 109 a-type, R-branch lines have been measured in the 355-638 GHz region and have been analyzed together with the low-J transitions observed by means of Fourier Transform microwave spectroscopy [H. Habara, S. Yamamoto, J. Mol. Spectrosc. 207 (2001) 238]. Twenty-one molecular constants have been determined accurately including the fine and hyperfine interaction constants. Comparison of the hyperfine constants with ab initio values and matrix electron spin resonance data has been made.     

Observation of bands among the four lowest pseudorotational states of 1,3-dioxolane

The rotational transitions belonging to the pseudorotational bands n=0→1, n=2→3, and n=0→3 have been experimentally observed for 1,3-dioxolane in the spectral region of 153-364 GHz in a supersonic jet environment using the FASSST absorption spectrometer. Based on these observations, the symmetry ordering and the energy spacings of the four lowest states, n=0,1,2,3, have been established. The totality of the available data on this molecule, including those available from previously reported microwave studies has been analyzed, and a set of molecular constants has been obtained. Using the newly determined frequencies of the pseudorotational bands, along with the frequencies of the previously reported pseudorotational bands in the IR spectrum region, an empirical potential surface of 1,3-dioxolane has been obtained. The results of this analysis are compared to the potential surface and rotational constants obtained from quantum chemistry calculations.     

Fourier transform microwave spectroscopy of N,N-dimethylacetamide

The jet-cooled Fourier-transform microwave spectrum of N,N-dimethylacetamide was recorded in the region of 12-24 GHz, and was analyzed to determine rotational constants and nuclear quadrupole coupling constants. Coriolis-like coupling parameters characterizing interaction between internal rotation of methyl groups and the overall rotation were also determined from internal-rotation tunneling splittings of the rotational transitions. The Coriolis-like coupling parameters permitted determination of the barrier heights to internal rotation of the three methyl groups, which were found to be 677, 237, and 183 cm⁻¹ for the C-methyl top, the trans-N-methyl top and the cis-N-methyl top, respectively.