Asao Mizoguchi

Rotational spectrum of a salt-containing van der Waals complex: Ar–NaCl

The first spectroscopic identification of a van der Waals complex containing salt, Ar–NaCl, has been reported. A cm-region rotational spectrum of the complex has been observed for the 35 Cl and 37 Cl isotopomers by using a Fourier-transform microwave spectrometer combined with a laser ablation nozzle source. The vibrationally averaged geometry of the complex is of the linear Ar⋯Na–Cl configuration, with the internuclear distance of R( Ar⋯Na )=2.887 A. An almost fully resolved hyperfine structure in low-J transitions has yielded precise nuclear quadrupole coupling constants associated with both Na and Cl nuclei, which indicate a substantial charge rearrangement in the NaCl molecule by complexation with Ar.

The study for the incipient solvation process of NaCl in water: The observation of the NaCl–(H2O)n (n = 1, 2, and 3) complexes using Fourier-transform microwave spectroscopy

Pure rotational spectra of the sodium chloride-water complexes, NaCl-(H(2)O)(n) (n = 1, 2, and 3), in the vibronic ground state have been observed by a Fourier- transform microwave spectrometer coupled with a laser ablation source. The (37)Cl-isotopic species and a few deuterated species have also been observed. From the analyses of the spectra, the rotational constants, the centrifugal distortion constants, and the nuclear quadrupole coupling constants of the Na and Cl nuclei were determined precisely for all the species. The molecular structures of NaCl-(H(2)O)(n) were determined using the rotational constants and the molecular symmetry. The charge distributions around Na and Cl nuclei in NaCl are dramatically changed by the complex formation with H(2)O. Prominent dependences of the bond lengths r(Na-Cl) on the number of H(2)O were also observed. By a comparison with results of theoretical studies, it is shown that the structure of NaCl-(H(2)O)(3) is approaching to that of the contact ion-pair, which is considered to be an intermediate species in the incipient solvation process.

van der Waals bending bands of the ArDCN cluster observed by millimeter-wave spectroscopy combined with a pulsed supersonic jet technique

Millimeter-wave absorption spectroscopy combined with a pulsed-jet expansion technique was applied to the measurement of the rovibrational transitions of the van der Waals (vdW) bending bands of the ArDCN cluster in the frequency region of 182∼294 GHz. Sixteen and thirty-seven rovibrational lines were observed for the Σ1–Σ0 and Π1–Σ0 bands, respectively, split into hyperfine structure due to the nitrogen nucleus. A set of accurate molecular constants, including the band origins, rotational constants, nuclear quadrupole coupling constants, and the Coriolis interaction constant between the Σ1 and Π1 bending substates, was determined. The band origins for the Σ1–Σ0 and Π1–Σ0 bands of ArDCN, 189.017 380(7) GHz and 195.550 736(12) GHz, are larger by 24.126 585(9) and 13.566 314(16) GHz than the corresponding values of ArHCN, respectively. The abnormal isotopic effect on the vibrational frequencies is attributed to the characteristic potential energy surface of ArH(D)CN, which has two minima, corresponding to t...

Interplay of methyl-group internal rotation and fine and hyperfine interaction in a free radical: Fourier transform microwave spectroscopy of the acetyl radical

The fine and hyperfine structure in a free radical containing a methyl group is examined by paying special attention to the effects of the methyl group internal rotation on the fine and hyperfine interactions. The effects are taken into account by expanding pertinent constants describing couplings among angular momenta of electron and nuclear spins, internal rotation and overall rotation in terms of the internal rotation angle. The three-fold symmetry of the methyl internal rotation potential is lifted to some extent by fine and hyperfine interactions. The formulation thus developed is applied to the analysis of Fourier transform microwave spectra of the acetyl radical, and the potential barrier to internal rotation [139.958 (18) cm−1] and fine and hyperfine interaction constants are determined precisely.

Detection of Microwave Transitions between Ortho and Para States in a Free Isolated Molecule

Microwave transitions between the ortho and para states of the S_{2}Cl_{2} molecule in a free isolated condition are observed for the first time. In the theoretical treatment, we derive eigenfunctions of an effective Hamiltonian including the ortho-para interaction to calculate the intensities and frequencies of forbidden ortho-para transitions in the cm-wave region and pick up some promising candidates for the spectroscopic detection. In the experiment, transitions of the S_{2}Cl_{2} molecule under a supersonic jet condition are observed with a Fourier transform microwave spectrometer. Seven hyperfine resolved rotational transitions including the lowest rotational level are detected as the ortho-para transitions at the predicted frequencies within the experimental errors. The observed intensities are about 10^{-3} times the allowed transitions, which are consistent with the predictions based on the intensity-borrowing model. This result suggests that the ortho-para conversion of this molecule occurs in a few thousand years through spontaneous emission even in a circumstance where molecular collisions occur rarely like in interstellar space.

DETECTION OF THE MW TRANSITION BETWEEN ORTHO AND PARA STATES

Thorough the detailed analysis of the hyperfine resolved rotational transitionsab, we have been pointed out that there exists not a little interaction between ortho and para states in the molecular Hamiltonian of S2Cl2. Using the ortho-para mixed molecular wavefunctions derived from the Hamiltonian, we calculated the transition moment and frequency of the ortho-para forbidden transitions in the cmand mm-wave region, and picked up some promising candidate transitions for the spectroscopic detection. In the experiment, the S2Cl2 vapor with Ar buffer gas in a supersonic jet condition was used with FTMW spectrometer at National Chiao Tung University. As a result, seven hyperfine resolved rotational transitions in the cm-wave region were detected as the ortho-para transition at the predicted frequency within the experimental error range. The observed intensity was 10−3 smaller than that of an allowed transition, which is also consistent with the prediction. This is the first time the electric dipole transition between ortho and para states has been detected in a free isolated molecule.

Millimeter-wave Spectroscopy Of S2cl2: A Candidate Molecule For The Detection Of Ortho-para Transition

S2Cl2 is a candidate molecule for the detection of ortho-para transition, because the Cl atoms on the skewed position from the rotational principle axes give large off-diagonal terms in the quadrupole interaction, which can mix ortho and para states. In order to estimate the ortho-para mixing in a hyperfine-resolved rotational state, pure rotational transitions were measured by millimeter-wave spectroscopy using two different experimental set-ups. The transitions from the term value around 20 K was measured with a supersonic jet and those around 200 K were measured with a dry ice cooled gas cell. Hundreds of peaks were assigned for the naturally abundant S2Cl2 and S2ClCl isotopic species, and the rotational molecular constants including the fourth-order and sixth-order centrifugal distortion constants were determined. The hyperfine structures were partly resolved in some Q-branch transitions and those spectral patterns were well reproduced with the hyperfine constants determined by the previous FTMW spectroscopy in the cm-wave regiona. With the new molecular constants determined in this study and the previous hyperfine constants, it becomes possible to predict a more reliable ortho-para mixing ratio and to narrow down the possible candidate transitions in the mm-wave region for the detection of ortho-para transition.

Millimeter-wave spectroscopy of S2Cl2: a candidate molecule for measuring ortho-para transition.

S2Cl2 is a candidate for the observation of ortho-para transition. To estimate the ortho-para mixing in a hyperfine-resolved rotational state, pure rotational transitions were measured by millimeter-wave (mm-wave) spectroscopy using two different experimental set-ups. The transitions from the term value around 20 K was measured with a supersonic jet and those around 200 K were measured with a dry ice cooled gas cell. Several hundred peaks were assigned for the naturally abundant S2(35)Cl2 and S2(35)Cl(37)Cl isotopic species and the rotational molecular parameters including the fourth-order and sixth-order centrifugal distortion constants were determined. The hyperfine structures were partly resolved in some Q-branch transitions, which were well described with the hyperfine constants determined by FTMW spectroscopy in the centimeter-wave region. With the new rotational constants determined in our study and the previous hyperfine constants, it will be possible to obtain a more reliable ortho-para mixing ratio and to narrow down the possible candidate transitions in the mm-wave region for the observation of ortho-para transition.