Shozo Tsunekawa

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.

Effective torsion-rotation Hamiltonian for methanol-type molecules

Abstract A fourth-order effective Hamiltonian has been derived for the torsion-rotation problem of a methanol-type molecule, i.e., for a C 3 v top attached to a C s frame. First, symmetry considerations based on a frame-fixed axis system are used to determine allowed terms in the Hamiltonian. These terms are then subjected to a contact transformation to remove the indeterminate ones. This procedure is essentially an extension of Watsons method for semirigid molecules to the torsion-rotation problem. It is demonstrated that the Hamiltonian derived in the present work is capable of improving the fittings of the millimeter and submillimeter absorption frequencies of CH 3 OH and CH 3 SH.

Torsionally Excited Methyl Formate in Orion KL

We report the first detection of rotational transitions of methyl formate (HCOOCH3) in the first torsionally excited state (vt = 1). Recent progress on the assignment of laboratory spectra of methyl formate made it possible for us to assign about 20 unidentified lines in Orion KL from previous line surveys below 200 GHz to the first torsionally excited methyl formate. The rotational temperature and column density obtained in the first torsionally excited state were 44 ± 10 K and (8.6 ± 3.2) × 1014 cm-2, respectively. They were compared with those in the ground state.

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.

Far-Infrared Spectroscopy of LiH using a Tunable Far-Infrared Spectrometer*

An Evenson-type tunable far-infrared spectrometer has been built to measure rotational transition frequencies of LiH up to 5 THz. R(J) transitions with J=0 to 10 (v=0) and J=1 to 10 (v=1) of 7LiH, and those with J=1 to 9 (v=0) of 6LiH have been measured. Frequency measurements with an accuracy of tens of kHz enable us to improve rotational parameters of LiH.

Microwave spectrum of acetamide

Abstract The microwave spectrum of acetamide was observed in the frequency range 12 to 40 GHz and was analyzed by the internal axis method. The dipole moment was determined from the Stark effect of E-species lines to be μ = 3.68 ± 0.03 D, with its components μz = −1.22 ± 0.01 D and μy = 3.47 ± 0.03 D. The line strength for each transition was calculated using both μz and μy. The analysis was carried out on the basis of our previously reported molecular constants (J. Mol. Spectrosc. 112, 494–495 (1985)): Ia = 46.9547(34), Ib = 54.1223(47), Ic = 97.9995(120), Iab = 1.4683(81), I a2 = 3.1732(39) u A 2 , and V3 = 24.631(29) cm−1. In the above expression, the a axis is parallel to the axis of the methyl top and the z axis is the internal rotation axis which makes an angle of tan−1 ( I ab I b ) with the a axis.

ANALYSIS OF THE MICROWAVE SPECTRUM OF HYDRAZINE

Abstract Microwave measurements in the interval from 6 to 133 GHz, consisting of 444 rotational transitions in the vibrational ground state of hydrazine with J ≤ 31 and K a ≤ 6 were fit to an effective rotational Hamiltonian containing 9 asymmetric rotor constants, 14 NH 2 inversion parameters, and 1 internal rotation parameter, with an overall standard deviation of the fit of 0.40 MHz. This set of parameters contains: (i) the three rotational constants; (ii) tunneling splitting constants for NH 2 inversion at one end of the molecule, for NH 2 inversion at both ends of the molecule, and for internal rotation through the trans barrier; (iii) two K -type doubling constants affecting the K = 1 levels; (iv) an a -type Coriolis interaction with matrix elements linear in K ; and (v) various centrifugal distortion corrections to the above parameters. A consistent group theoretical formalism was used to label the energy levels and to select terms in the phenomenological rotational Hamiltonian. The Hamiltonian matrix, which is set up in a tunneling basis set, is of dimension 16×16 and contains only Δ K a = 0 matrix elements, asymmetric rotor effects being taken into account on the diagonal by terms from a Polo expansion in b n . Hyperfine splittings and barrier heights are not discussed.

Laboratory Microwave Spectrum of CH318OH

The microwave spectrum of CH318OH has been observed in the frequency range from 95 to 200 GHz. This observation is an extension of the one made by Hoshino et al. in the frequency range below 95 GHz. Observed lines are those with J ≤ 39, K ≤ 8 for the A-species and with J ≤ 42, |K| ≤ 7 for the E-species in the torsional ground state (vt = 0) and some lines in the torsional excited state (vt = 1-3). A total of 533 microwave lines with vt ≤ 2, J ≤ 42, and K ≤ 8 have been fitted to 66 molecular constants by using the reduced Hamiltonian (Tang & Takagi) with a root mean square (rms) of 0.271 MHz, where the A and E substates are treated simultaneously. Three unidentified interstellar lines have been assigned to CH318OH lines tentatively.

The Microwave Spectroscopy of Methyl Formate in the Second Torsional Excited State

The cis-methyl formate molecule is a well known molecule found in interstellar space. Recently, rotational lines of methyl formate in the first CH3 torsional excited state were observed in Orion KL and W51e2. It is quite natural to observe methyl formate in even higher vibrational states considering the temperature estimated in Orion KL and W51e2. Maeda et al. reported results on the laboratory spectroscopy of methyl formate including the spectral analysis in its second CH3 torsional state. Their assignments were limited to a series of a-type R-branch lines and low Ka b-type R-branch transitions, and many assigned lines are excluded in the least-squares analysis. In the present study, we extended the line assignments of both the A- and E-species transitions in the second CH3 torsional state especially in the frequency region below the 120?GHz region. By combining the present assignments and those made by Maeda et al., 1951 transitions in total for the second CH3 torsional state, 1096 A-species transitions up to J = 39, and Ka = 15 and 855 E-species transitions up to J = 35 and Ka = 13, were least-squares analyzed by using the pseudo-principal-axis-method Hamiltonian with 42 parameters consisting of rotational, centrifugal distortion, and internal rotational constants in the second CH3 torsional state. In addition, 1012 transitions out of 1096 A-species transitions could also be least-squares analyzed by using Watsons A-reduced Hamiltonian with 43 parameters, which can serve to calculate the energy levels of the A-species lines of molecules with the CH3 internal rotation conveniently.

Analysis of Rotational Transitions of Methyl Formate in the Ground and First Excited Torsional States

The microwave spectrum of methyl formate has been observed in the 7−200 GHz region, and new 437 lines have been assigned to the first excited A torsional substate. Both excited state lines and ground state lines reported previously were analyzed simultaneously on the basis of an internal axis method Hamiltonian. A total of 3514 lines were fitted to a 10th-order reduced Hamiltonian model involving 67 molecular parameters to a 1σ standard deviation of 179 kHz.