Hitoshi Odashima

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 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.

Tunable far-infrared spectroscopy extended to 9.1 THz

We synthesized tunable far-infrared radiation at frequencies higher than 9 THz (300 cm (-1)) by mixing CO(2) laser, (15)NH(3) laser, and microwave radiation in a W-Co metal-insulator-metal diode. We used this farinfrared radiation to accurately measure torsion-rotation transitions of CH(3)OH in the 8-9-THz region. We also measured the frequency of the aP(7, 3) (15)NH(3) laser transition.

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.

Microwave Spectrum of the Ethylmethyl Ether Molecule

We have observed rotational transitions of ethylmethyl ether (CH3CH2OCH3) in the 24-110 GHz frequency range. We newly assigned the transitions of four Q-branch series for J=1-38 with Ka=0-5 and six R-branch series of b-type transitions for J=7-37 with Ka=0-3. All these assigned transitions were observed to be split into two or four components due to the internal rotations of the methyl groups. We analyzed the averaged frequencies of the split components on the basis of the Watson A-reduced Hamiltonian, neglecting the effect of the internal rotations. A total of 122 transitions were fitted to eight molecular parameters to a 1σ standard deviation of 24 kHz. The parameters A, B, C and DJ were improved, and DJK, Dk, dJ and dK were determined for the first time.

Extension of tunable far-infrared spectroscopy to 7.9 THz

We generated tunable far-infrared radiation by mixing CO(2) -laser,(15)NH(3) -laser, and microwave radiations in a W-Co metal-insulator-metal diode. We used this far-infrared radiation to measure accurately the torsion-rotation transitions of CH(3)OH in the 6-8-THz region.

Dynamic Properties of Polar Molecules Confined in Electrostatic Trap

We theoretically investigate the dynamics of linear polar molecules in static quadrupole electric fields. Numerical calculation shows that molecules rotating in a specific direction experience a restoring force, being three-dimensionally trapped in the center of the field distribution. We formulate the probability of Majorana transition and the trapping lifetime with a simple model of a rotating dipole. Potential depth of the electrostatic trap is quantum-mechanically estimated to be in the order of 100 mK.

Characteristics of metal-insulator-metal diodes as generators of far-infrared radiation

Characteristics of metal-insulator-metal (MIM) diodes which are used as mixer-generators of far-infrared (FIR) radiation have been investigated for nine different diode base metals. It was found that a W-Fe diode works as effectively as a W-Co diode in generating tunable FIR radiation by mixing two CO/sub 2/ lasers and microwave radiation. The bias dependences of W-Ni, W-Co, and W-Fe MIM diodes have also been examined. Observed bias results can be predicted by analyzing their current-voltage characteristics.

Flow-Assisted Optical Trapping of Microparticle Produced by Laser Ablation

With a goal for application to terahertz spectroscopy, we develop an optical trap with retroreflected CO2 laser beams that suspends microparticles of organic molecular crystals in a gas medium. Laser ablation with trapping radiation decomposes coarse-grained samples into micrometer-sized particles. We demonstrate that a consistent upward airflow partly cancels gravity and markedly improves the stability of optical levitation.