Kojiro Takagi

Frequency measurement of pure rotational transitions of H2O from 0.5 to 5 THz

Frequencies of H20 pure rotational transitions from 0.5 to 5 THz have been measured with an accuracy of one part in 108 using a tunable far-infrared spectrometer. Measured frequencies of more than a hundred spectral lines provide an excellent wavelength and frequency calibration standard for the far-infrared. A set of molecular parameters based on a Watson-type Hamiltonian has been obtained to reproduce the observed frequencies.

Far-infrared spectrum and ground state constants of methyl amine

Abstract 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.

Separation and conversion dynamics of four nuclear spin isomers of ethylene.

Molecules with three or more nuclei of nonzero spin exist as discrete spin isomers whose interconversion in the gas phase is generally considered improbable. We have studied the interconversion process in ethylene by creating a sample depleted in the B2u nuclear spin isomer. The separation was achieved through spatial drift of this isomer induced by resonant absorption of narrow-band infrared light. Evolution of the depleted sample revealed conversion between B2u and B3u isomers at a rate linearly proportional to pressure, with a rate constant of 5.5 (±0.8) × 10–4 s–1 torr–1. However, almost no change was observed in the Ag isomer populations. The results suggest a spin conversion mechanism in C2H4 via quantum relaxation within the same inversion symmetry.

Microwave spectrum of methyl amine: Assignment and analysis of the first torsional state

Abstract The microwave absorption spectrum of methyl amine has been reinvestigated in the range from 7 to 90 GHz, with the aim of analyzing the first torsional state in more detail. By combining the newly obtained microwave data with the far-infrared and microwave data already available, it was possible to make and analysis of the tunneling-rotational levels of the first torsional state in which three types of Δ K = ±1 elements were introduced into the Hamiltonian matrix described in the group-theoretical formalism developed previously. The present global fit uses 38 molecular parameters (three fewer than previously) to describe 714 transitions involving tunneling-rotational levels of the first excited torsional state (57 more than previously). It resulted in a satisfactorily small standard deviation of 0.00095 cm −1 (almost the same as previously) for J ≦ 30 (five J values higher than included previously). On the basis of this fit, avoided crossings between K = 0 and 1 levels belonging to A and B species in the molecular symmetry group G 12 are discussed in detail for the first time. Stark effect data, remeasured during the present study, are also examined in connection with the Δ K = ±1 interaction.

Higher‐order effects in the vibration–torsion–rotation spectra of a molecule with an internal rotor

The sequential contact transformation technique is applied to the vibrational–torsional–rotational Hamiltonian for molecules containing a threefold symmetric internal rotor, which makes it possible to analyze various higher‐order vibration–torsion–rotation interactions and their effects in the vibration–torsion–rotation spectra of the molecule. The formalism for the calculation of Hamiltonian coefficients is developed in terms of the fundamental molecular parameters. The resulting formulas are applicable to analyze the molecular structure. The theory presented is applied to the calculation of the quartic and sixtic centrifugal distortion constants of the molecule.

Microwave spectrum of nitroxyl

Abstract The microwave spectrum of HNO has been observed and analyzed. Both a -type and b -type transitions have been measured. The rotational constants obtained are A = 553903.0 ± 2.7 MHz, B = 42308.52 ± 0.10 MHz, and C = 39169.46 ± 0.10 MHz. In the analysis of the spectrum, centrifugal distortion corrections are tentatively taken into account by using the centrifugal distortion constants determined by Dalby. The quadrupole coupling constants for nitrogen in HNO are determined to be χ aa = 0.36 ± 0.56 MHz, χ bb = − 5.46 ± 0.30 MHz, and χ cc = 5.10 ± 0.26 MHz. The dipole moment and its components determined from the Stark effect measurement are μ total = 1.67 ± 0.03 D, μ a = 1.03 ± 0.01 D, and μ b = 1.31 ± 0.02 D. The microwave spectrum of DNO has been reanalyzed by taking into account the centrifugal distortion effect. The inertia defects for HNO and DNO have been calculated. The results are limited in precision by the lack of reliable force constants.

Correlation problems and a correlation-free torsion-rotation Hamiltonian for a molecule with an internal rotor

To develop a correlation-free reduced form of torsion-rotation Hamiltonian that is suitable for analyzing observed spectra for methanol and its isotopic species, the origin of various classes of correlation problems often encountered in fitting the molecular constants to experimental data are analyzed for a molecule with an internal rotation. It is shown that the correlation problems can be completely eliminated by considering either the data set or the reduction of the Hamiltonian together with practical considerations, where an appropriate definition of order of magnitude plays an important role. For a molecule with C3v(M) symmetry such as methanol and its isotopic species, it is found that some terms which are included in the traditional or a reduced Hamiltonian given so far should not be used simultaneously. For example, the traditional terms k5Pa2(1−cos 3γ) and k6Pa{Pγ,1−cos 3γ} should not be used simultaneously as adjustable ones and one of three traditional terms k6Pa{Pγ,1−cos 3γ}, k7{Pγ2,1−cos 3γ}...

Microwave optical double resonance of HNO: Rotational spectrum in Ã1A′′(100).

Rotational transitions in the ?1A″(100) state of HNO were observed using the technique of microwave optical double resonance. The HNO molecule was produced in a fast flow system by the reaction of discharged oxygen with a mixture of propylene and NO. Eighteen rotational lines observed in the frequency regions of 8 to 157 GHz and rf were analyzed to give rotational constants and centrifugal distortion constants. Perturbations were found in the K‐type doubling frequencies of K−1 =1 and 2.

The calculation of molecular parameters for a molecule with an internal rotor

A derivation for the formulas to calculate centrifugal distortion constants, based on a recent formulation [Duan and Takagi, Phys. Lett. A (1995)] of centrifugal distortion effects for a molecule containing a threefold symmetric internal rotor, is presented. Some constants which are independent of the barrier derivatives, especially the constants representing interactions between torsion and rotation, are given in terms of molecular structural parameters and force constants. These calculated constants are helpful in the reduction of the Hamiltonian and in the analysis of observed transitions. The derived formulas are applied to numerical calculations of the centrifugal distortion constants of methanol. It is shown that most of the calculated constants are in good agreement with those obtained from the fitting to experimental data.

Microwave spectrum of CH3OD

Abstract The microwave spectrum of CH 3 OD has been observed in the frequency region between 14 and 92 GHz. All the ground-state transitions with J ≤ 8 and J = 2 ← 1, a -type transitions in the excited torsional states ( v = 1 and v = 2) have been observed. The spectrum has been analyzed and rotational constants, torsional constants, torsion-vibration-rotation interaction constants, and centrifugal distortion constants have been evaluated. The Stark effect measurements have been made and the dipole moment components have been determined as μ a = 0.833 ± 0.008 D and μ b = 1.488 ± 0.015 D .