Masao Onda

Microwave spectrum, structure, and electric dipole moment of ArCH3OH

Abstract Microwave spectra of ArCH3OH, ArCD3OH, and Ar13CH3OH have been measured between 7 and 25 GHz using a pulsed-nozzle Fourier transform microwave spectrometer. Two tunneling states are observed which correlate to the A and E internal-rotor states of free methanol. For the lowest energy A state, a- and b-type spectra are assigned and fitted to an asymmetrical-top Hamiltonian, giving A = 25 468.821(4) MHz, B = 2084.42(2) MHz, C = 1928.46(2) MHz, ΔJ = 21.90(2) kHz, ΔJK = 371.7(1) kHz, δK = 474(10) kHz, δJ = 1.61(8) kHz, and hK = 10.1(8) kHz for ArCH3OH. The electric-dipole-moment components, μa and μb, are determined by Stark-effect measurements to be 1.079(1) and 1.069(5) D, respectively. The Stark-effect results and the absence of c-type transitions indicate that μc ∼ 0. The structure of the complex is found to be T-shaped with an Ar to CH3OH center-of-mass separation of 3.684(14) A. The inertial defect, Δ = −0.2347 u A 2 , is surprisingly small and suggests that the methanol unit is internally rotating against the Ar. This is in addition to the internal rotation of the CH3 group against the OH top. Finally, a number of transitions are observed which do not appear to fit an asymmetrical-top Hamiltonian. These are assigned to an E tunneling state of the complex.

Microwave spectrum of catechol (1,2-dihydroxybenzene)

Abstract The microwave spectra of the normal species and three deuterated species of catechol have been observed in the frequency ranges 8–18.6 and 26.5–40 GHz. The inertial defect and the r s coordinates of the hydrogen obtained from the assigned spectra indicate that the conformation of the molecule is planar with intramolecular hydrogen bonding. A measure of the strength of the hydrogen bond is proposed from the difference of inertial defects in OH and OD species; the strength estimated for catechol almost equals that in 2-chlorophenol.

MICROWAVE SPECTRUM AND MOLECULAR PLANARITY OF ACETOPHENONE

Abstract The microwave spectrum of acetophenone was observed in the frequency region 9–18 GHz. The rotational and centrifugal distortion constants of acetophenone in the ground and first three excited states of torsion around the CCOCH3 bond have been determined. The determined constants for the ground state are A = 3688.040(11) MHz, B = 1215.048(1) MHz, C = 919.919(1) MHz, ΔJK = −0.250(44) kHz, ΔK = 1.95(68) kHz, and δK = 0.440(22) kHz. The residual inertial defect calculated from the inertial defects of the ground and torsional excited states indicates that the structure of acetophenone is skeletal planar.

Microwave spectra and structure of 1,2-dichlorobenzene-3d and -4d

Abstract The microwave spectra of six monodeuterated 1,2-dichlorobenzenes-3 d and -4 d , each having 1,2- 35 Cl 2 , 1,2- 35 Cl 37 Cl, or 1,2- 37 Cl 35 Cl, in the frequency range 10–40 GHz, have been analyzed. The r 0 -structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r 0 bond lengths (A) and bond angles (degrees) are as follows: r CC = 1.393–1.398; r CH = 1.080–1.083; r CCl = 1.729(15); ∠CCC = 119.5–120.3; ∠C(1)C(2)Cl(2) = 120.9(5); ∠C(2)C(3)H(3) = 118.7(11); and ∠C(3)C(4)H(4) = 119.5(13). The following distortions in the structure are found. The distortion of the benzene ring is of the same extent as in chlorobenzene and rather smaller than in fluorobenzenes. On the other hand, the two CCl bonds bend outwards from each other by about 1° and the ortho -hydrogen H(3) by 0.6° towards the Cl atom, respectively, from the bisector at the ipso -carbon. The ortho -hydrogen is closer to the chlorine atom. The possibility of a “bent bond” in the CCl has been inspected from the nuclear quadrupole coupling constants of chlorine nuclei.

Microwave spectrum,structure and quadrupole coupling constants of o-dichlorobenzene

Abstract The microwave spectrum of two isotopic species of o -dichlorobenzene, C 6 H 4 35 Cl 2 and C 6 H 4 35 Cl 37 Cl, have been studied. The R -branches of the a-type transition lines in the 8–35 GHz region have been assigned for the ground and first three excited vibrational states of the C-Cl out-of-plane bending mode (A 2 ). The small inertia defect obtained indicates that the molecule is planar. The non-bonded ClβCl distance was obtained using the Kraitchman equation, and the structure of the molecule is discussed. The quadrupole coupling constants of the chlorine nucleus were obtained by measurements of the envelope of the hyperfine structure. The results are χ aa = −37.9 ± 1.3 MHz, χ bb = 7.0 ± 0.7 MHz, and χ cc = 30.9 ± 2.0 MHz for 35 Cl.

Microwave spectrum and the structure of benzoyl chloride

Abstract The microwave spectrum of benzoyl chloride was observed in the frequency range 12–18.6 GHz. Rotational constants have been obtained for the ground vibrational state, the first three excited torsional states of the COCl group, and one of the out-of-plane bending states. The residual inertial defect obtained from the ground and the torsional excited states indicates that the equilibrium conformation is planar. Ab initio MO calculations (STO-3G) showed the potential energy curve as a function of the COCl torsional angle to be rather flat around zero degrees.

Microwave spectroscopic study on the molecular structure and the quadrupole coupling constants of thionyl chloride

Abstract Microwave spectra of thionyl chloride, SO35Cl2 and SO35Cl37Cl, in the frequency range 8–25 GHz have been analyzed. The rotational constants have been obtained from the low J transition frequencies. The rS coordinates of Cl atoms and the ro structure have been evaluated with some assumptions: r(S-O) = 1.435 ± 0.011± A, r(S—Cl) = 2.072 0.005 A, ∠ OSCl = 108.00 ± 0.06°, ∠ ClSCl = 97.15 ± 0.30°. Nuclear quadrupole coupling constants have been obtained for the SO35Cl2, species: xaa = −25.02 ± 0.04 MHz, x(bb = −0.25 ± 0.04 MHz, Xcc = 25.27 ± 0.08 MHz, and Xzz = −96.75 MHz. The values obtained are compared with those of other workers.

Microwave spectra and structure of 1,3-dichlorobenzene

Abstract The microwave spectra of 1,3-dichlorobenzenes (35Cl2 and 35Cl37Cl) and their six monodeuterated species have been observed and analyzed in the frequency range 10–40 GHz. The r0 structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r0 bond lengths (in pm) and bond angles (in degrees) are as follows: rCC = 138.9–139.5, rCH = 108.3–110.8, rCCl = 172.7(35), ∠ CCC 118.9–121.0, ∠ Cl(7)C(1)C(2) = 119.2(36), ∠C(3)C(4)H(10) = 118.4(44). The following distortions in the structure have been found: the distortion of the benzene ring is of the same extent as in chlorobenzene (CCC angles are 119.4–120.7°) and ortho-hydrogen H(10) is located close to the chlorine atom.

Microwave spectra and conformation of trans-2-butenoic acid

Abstract Microwave spectra of trans -2-butenoic acid (crotonic acid) and its deuterated species have been investigated. Analysis of the spectra reveals that this molecule exists in two forms, s-trans and s-cis , in the gas phase. The r s coordinates of the hydrogen atom in the OH group have been determined. The barriers to methyl internal rotation are 1830 and 1750 cal mol −1 for the s-trans and s-cis forms, respectively. The dipole moment of this molecule was estimated from ab initio calculation and from this the ratio of the amounts of the two conformers was estimated.

The microwave spectrum and dipole moment of pentafluorobenzene

The microwave spectrum of pentafluorobenzene was reported by Doraiswamy and Sharma in 1974 [l]. They determined its dipole moment as 144(5)D from the Stark effect of only one component, M = 1, of the 3(3,1)-2(2,0) transition. They found that most of the low J lines of the R-branch were in congested regions of the spectrum (8-12.4 GHz). This situation is often encountered for rather large molecules, such as substituted benzenes, due to their small rotational constants and many low lying vibrational states. In 1982, Doraiswamy also reported the centrifugal distortion constants and structure of this molecule t21. Here, we present the redetermination of the dipole moment with improved accuracy from the Stark coefficient of low-J transitions measured using a molecular beam Fourier transform spectrometer. The rotational transitions were measured using a home-made Balle-Flygare type molecular beam-FT-microwave spectrometer [3]. A single microwave source system was adapted similarly to the one constructed by Suenram et al. [4]. The frequency region of the spectrometer in this investigation was 614GHz.