Yoshiki Okada

Reactions of protonated water clusters H+(H2O)n (n=1–6) with dimethylsulfoxide in a guided ion beam apparatus

Abstract Reaction cross sections for the reactions of protonated water clusters, H + (H 2 O) n ( n =1–6) with dimethylsulfoxide (DMSO) were measured at the collision energy of 0.1 eV. The cross section at n =2, which was found to be twice as large as that at n =4, showed a possibility of direct proton transfer process. The proton is likely to transfer directly from H + (H 2 O) 2 to DMSO without forming an intermediate complex because of the larger proton affinity of DMSO than that of water dimer.

A Differential Mobility Analyzer and a Faraday Cup Electrometer for Operation at 200-930 Pa Pressure

Abstract We have developed a differential mobility analyzer (DMA) based on the DMA devised by Seto et al. (1997) and a Faraday cup electrometer for measurement of nanometer-sized particles at a few hundred Pa and examined the operating characteristics of the DMA using the tandem DMA technique. The tandem DMA calibration establishes that the DMA successfully classifies particles in the 200–930 Pa pressure range. It was also found that the transfer function of the DMA follows the triangular transfer function and the resolution of the DMA is close to that given for an ideal case. As a standard of a minimum pressure that may be probed with the present DMA system, 400 Pa is estimated when the DMA operates with a 3 nl min −1 sheath flow and a 1 nl min −1 aerosol flow rate.

Collisional reaction of water cluster cations (H2O)n+ (n=2 and 3) with D2O

Abstract Collisional reactions of size- and energy-selected unprotonated water clusters (H 2 O) n + ( n =2 and 3) in a single-collision with D 2 O were investigated at very low collision energy ranging from 0.05 to 2.0 eV using guided-ion beam tandem mass spectrometry. First, in the unimolecular and collision-induced dissociations of (H 2 O) 2 + and (H 2 O) 3 + , only the H 2 O + fragment, but not the H 3 O + fragment, was observed. These results suggest that the structure of (H 2 O) 2 + is primarily hemibonded ‘(H 2 O⋯OH 2 ) + ’ rather than proton-transferred ‘(H 3 O + ⋯OH)’. Second, the measured incorporation cross-section of (H 2 O) 2 + was found to be smaller than that of H + (H 2 O) 2 . From the dipole moment obtained by ab initio calculation, we found that the small values of the incorporation cross-section for (H 2 O) 2 + were caused by the small value, 0.0 debye, of the dipole moment of the cluster.

Aerosol spectrometer for size and composition analysis of nanoparticles

Abstract We describe the design and performance of a spectrometer that simultaneously measures the size-dependent concentration and chemical composition of particles ranging from 5 to 40 nm . The spectrometer consists of a differential mobility analyzer for size analysis and an inductively coupled plasma mass spectrometer for composition analysis. For a particle size of 30 nm , the lower detection limit of the spectrometer for particle concentration is about 1×10 5 particles cm −3 .

ADAPTIVE INTERNAL MODEL CONTROL AND ITS APPLICATION TO A BATCH POLYMERIZATION REACTOR

Abstract In this paper, the internal model control (IMC) and the adaptive parameter identification technique by the model refernece adaptive system (MRAS) are newly combined, and the combined one is called the adaptive IMC (AIMC). The proposed AIMC inherits the advantageous points from IMC, e.g., easiness to evaluate the robustness of the modelling error and to design a filter of an AIMC taking into account of its robustness. Moreover, parameters of the internal model are adjusted by MRAS in the proposed scheme. Then, the system can be controlled perfectly if the order of the system is appropriately assumed and if the system is a minimum phase one. One more advantageous point which is most significant one in practical application of the AIMC is; if the model is taken as 1st order system, the AIMC can be reduced to an auto-tuning proportional-plus-integral (PI) feedback controller. The proposed AIMC is applied to the control of a batch polymerization reactor. Temperature of the reactor is controlled so as to follow the desired temperature profile by the AIMC. The system equation of the batch reactor is time-dependent, and parameter adaptation will be required for getting a sophisticated controller. For this problem, the proposed AIMC can be utilized successfully and is shown to be superior compared with a traditional PI controller by the computer simulation.

Reaction cross section for incorporation of ND3 into NH4+(NH3)n−1 (n=3–9) at very low energy collision

Cross sections for the collision-induced reactions between protonated ammonia cluster ions, NH4+(NH3)n−1 (n=3–9), with ND3 were measured at a collision energy ranging from 0.02 to 1.4 eV in the center-of-mass frame with an extremely narrow energy distribution of 0.02 eV. Two types of reaction, incorporation and dissociation, were observed at the same collision energy. The incorporation cross section increased drastically with a decrease in the collision energy, especially in the collision energy region below about 0.2 eV. The incorporation cross section at a collision energy of about 0.02 eV was larger than twice the geometrical reaction cross section. It is suggested that the increase of the incorporation cross section corresponds to the increase of the collision cross section between the cluster ion and the neutral molecule at the low collision energies used in this study because of the presence of the electrostatic attractive force. The reaction probability for incorporation also increased with a decre...

Short-time Fourier transform analysis of ab initio molecular dynamics simulation: Collision reaction between NH4+(NH3)2 and NH3

An analyzing technique of the ab initio molecular dynamics simulation is proposed with the use of short-time Fourier transform (ST-FT). The ST-FT analysis demonstrates the dynamical change of the vibrational states in the simulated system. Numerical assessments are preformed for the collision reaction of the ammonia cluster ion NH+(4) (NH3)(2) with the ammonia monomer NH3. Spectrogram obtained by the ST-FT method, which corresponds to the time evolution of vibrational power spectra, clarifies the relationship between the vibrational states and the reaction channels such as nonreactive collision, substitution, and incorporation.

Cluster size dependence of the H/D exchange reaction rate constant for protonated water clusters H+(H2O)n (n=2–11)

Abstract The collisions of size- and energy-selected H + (H 2 O) n ( n =2–11) with D 2 O have been investigated using guided-ion beam mass spectrometry. The H/D exchange reaction was observed by incorporation of D 2 O into H + (H 2 O) n . The measured rate constants of this reaction are found to depend strongly on the cluster size; the rate constants drastically decrease up to n =6, and then level off for 6⩽ n ⩽11. This size dependence is discussed in terms of the structure of protonated water clusters: the core H 3 O + and H 5 O 2 + ions, so-called Eigen and Zundel cations respectively, are completely surrounded by the first water layer and cause the rate constants for 6⩽ n ⩽11 essentially insensitive to n .

Laser isotope separation of heavy elements by infrared multiphoton dissociation of metal alkoxides

Abstract The molecular laser isotope separation (MLIS) of germanium and zirconium was investigated by TEA CO 2 laser-induced infrared multiphoton dissociation (IRMPD) of germanium tetramethoxide (Ge(OCH 3 ) 4 ) and zirconium tetra-tert-butoxide (Zr[OC(CH 3 ) 3 ] 4 ). Ge(OCH 3 ) 4 at 0.5 Torr was irradiated with a TEA CO 2 laser and the maximum of dissociation was observed around 1040 cm −1 . The critical fluence for the complete dissociation was found to be as low as 0.86 L/cm 2 near the optimum dissociation wavelength. A separation factor for 70 Ge with respect to 74 Ge was 1.8 by irradiation with the 9P(28) line (1039 cm −1 ) at room temperature. When 0.5 Torr of Zr[OC(CH 3 ) 3 ] 4 was irradiated at 80 °C with a TEA CO 2 laser, the dissociation maximum was found around 984 cm −1 . The critical fluence for the complete dissociation was estimated to be about 0.94 L/cm 2 near 984 cm −1 . Selective dissociation of specific Zr isotopes was not observed at 80 °C within the detection limit of mass spectrometer.

Theoretical study on ammonia cluster ions: Nature of kinetic magic number

We theoretically investigated collision cross sections due to the attractive forces between NH4+(NH3)n−1 (n=2–8) and ND3. We found that the dependence of the collision cross sections on collision energy and cluster size are comparable to those of measured fusion cross sections. The kinetic magic number, n=5, is related to the structure of the pentamer. Namely, the center ion in the pentamer is surrounded by first-shell ammonia molecules.