Fusakazu Matsushima

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.

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.

Submillimeter-wave and far-infrared spectroscopy of high-J transitions of the ground and ν2=1 states of ammonia

Complete and reliable knowledge of the ammonia spectrum is needed to enable the analysis and interpretation of astrophysical and planetary observations. Ammonia has been observed in the interstellar medium up to J=18 and more highly excited transitions are expected to appear in hot exoplanets and brown dwarfs. As a result, there is considerable interest in observing and assigning the high J (rovibrational) spectrum. In this work, numerous spectroscopic techniques were employed to study its high J transitions in the ground and ν(2)=1 states. Measurements were carried out using a frequency multiplied submillimeter spectrometer at Jet Propulsion Laboratory (JPL), a tunable far-infrared spectrometer at University of Toyama, and a high-resolution Bruker IFS 125 Fourier transform spectrometer (FTS) at Synchrotron SOLEIL. Highly excited ammonia was created with a radiofrequency discharge and a dc discharge, which allowed assignments of transitions with J up to 35. One hundred and seventy seven ground state and ν(2)=1 inversion transitions were observed with microwave accuracy in the 0.3-4.7 THz region. Of these, 125 were observed for the first time, including 26 ΔK=3 transitions. Over 2000 far-infrared transitions were assigned to the ground state and ν(2)=1 inversion bands as well as the ν(2) fundamental band. Of these, 1912 were assigned using the FTS data for the first time, including 222 ΔK=3 transitions. The accuracy of these measurements has been estimated to be 0.0003-0.0006 cm(-1). A reduced root mean square error of 0.9 was obtained for a global fit of the ground and ν(2)=1 states, which includes the lines assigned in this work and all previously available microwave, terahertz, far-infrared, and mid-infrared data. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA. The comprehensive experimental rovibrational energy levels reported here will permit further refinement of the potential energy surface to improve ammonia ab initio calculations and facilitate assignment of new high-resolution spectra of hot ammonia.

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.

Atomic oxygen fine-structure splittings with tunable far-infrared spectroscopy

We have accurately measured fine-structure splittings of atomic oxygen (l60) in the ground state using a tunable far-infrared spectrometer. The 3P,-3P, splitting is 2,060,069.09 (10) MHz, and the 3P1-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in Earths atmosphere and the interstellar medium. Subject headings: infrared: spectra - interstellar: matter - laboratory spectra - planets: atmospheres

Rotational spectra of 20NeH+, 20NeD+, 22NeH+, and 22NeD+

Rotational transitions of 20NeH+, 20NeD+, 22NeH+, and 22NeD+ were observed in the 1–5 THz frequency region with a high-precision far-infrared spectrometer using a tunable radiation source. Observed frequencies were incorporated with previous infrared measurement to redetermine Dunham coefficients Ykl and isotopically independent parameters Ukl, ΔklH, and ΔklNe, where Δ02H and Δ01Ne were determined for the first time.

Infrared–microwave double-resonance spectroscopy of CH 3 OH by use of sidebands of CO 2 laser lines

An infrared–microwave double-resonance technique using microwave sidebands of CO2 laser lines as an infrared source has been applied for observation of rotational lines of the methanol molecule. Frequencies of more than 50 rotational lines in the excited C—O stretching vibrational state (vco=1) have been measured with good precision and have been compared with those reported in infrared studies. Many of them agree within several megahertz, although some lines show differences of >10 MHz. The pressure dependence of the double-resonance signals for two low-J microwave transitions belonging to the ground and the vco=1 states, respectively, have been observed for sample pressures as high as 0.4 Torr. For the former transition the signal has been observed to change its sign at higher pressures. Rate equation analysis explains the observed pressure dependence quantitatively and allows us to understand the physical processes involved in the double resonance.

Molecular Beam Studies of Thermal Decomposition of Glycine on Solid Surfaces

A molecular beam technique for studying the decomposition of vapor-phase glycine on solid surfaces has been developed. The decomposition probability of glycine on the surfaces of polycrystalline molybdenum oxide and glass was measured as a function of the surface temperature. Decomposition products were quantitatively analyzed with a mass spectrometer in the temperature range of 420–800 K. The probability of decomposition of glycine per one collision with molybdenum oxide was found to be almost unity at a high surface temperature (~800 K), while that with glass was less than 0.15 in the observed temperature range. The values of activation energy E and the pre-exponential factor SZ2/Z1 for the decomposition are determined. A new model based on the transition state theory to evaluate the values of the pre-exponential factor is proposed.

Spectroscopic determination of fundamental molecular parameters for methanol and its isotopomers

Abstract An approach is presented, in which such fundamental molecular parameters as geometric structural parameters and potential ones are used to analyze observed spectra of a molecule with an internal rotor. As an example, geometric structural parameters, harmonic vibrational force constants, barrier heights to the internal rotation, and barrier derivatives with respect to molecular internal coordinates are determined by fitting them to observed torsion–rotational spectra for methanol and its isotopomers. By using these determined parameters, all the unreduced torsion–rotational molecular constants up to fourth order are calculated numerically.

DETECTION of HF TOWARD PKS 1830-211, SEARCH for INTERSTELLAR H2F+, and LABORATORY STUDY of H2F+ and H2Cl+ DISSOCIATIVE RECOMBINATION

We report extragalactic observations of two fluorine-bearing species, hydrogen fluoride (HF) and fluoronium (H2F+), in the z = 0.89 absorber in front of the lensed blazar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array. HF was detected toward both southwest and northeast images of the blazar, with column densities >3.4 × 1014 cm-2 and 0.18 × 1014 cm-2, respectively. H2F+ was not detected, down to an upper limit (3?) of 8.8 × 1011 cm-2 and an abundance ratio of [H2F+]/[HF] 1/386. We also searched for H2F+ toward the Galactic sources NGC 6334 I and W51C, and toward Galactic center clouds with the Herschel HIFI spectrometer.6 The upper limit on the column density was derived to be 2.5 × 1011 cm-2 in NGC 6334 I, which is 1/68 of that for H2Cl+. In constrast, the ortho transition of H2Cl+ is detected toward PKS 1830-211. To understand the small abundance of interstellar H2F+, we carried out laboratory experiments to determine the rate constants for the ion-electron recombination reaction by infrared time-resolved spectroscopy. The constants determined are ke(209 K) = (1.1 ± 0.3) ×10-7 cm3 s-1 and (0.46 ± 0.05) ×10-7 cm3 s-1 for H2F+ and H2Cl+, respectively. The difference in the dissociative recombination rates between H2F+ and H2Cl+ by a factor ?2 and the cosmic abundance ratio [F]/[Cl] ? 1/6 are not enough to explain the much smaller abundance of H2F+. The difference in the formation mechanism of H2F+ and H2Cl+ in interstellar space would be a major factor in the small abundance of H2F+.