Hidekazu Nagai

Spontaneous ignition limits of silane and phosphine

Abstract Spontaneous ignition limits of silane and phosphine have been investigated at relatively low concentrations. For silane, the spontaneous ignition occurs if the mixture concentrations is such that the silane/oxygen ratio is higher than a certain threshold limit value. In other words, the mixture is not stable if the ratio is higher than a certain value. On the other hand, in the case of phosphine the threshold limit line has been found to be a little curved, though the reason for the fact is not clear. At any rate, it is concluded that the spontaneous ignition of both silane and phosphine occurs as a result of a competition of chain branching and chain breaking reactions, in a way that is qualitatively similar to that in hydrogen oxidation.

Optical–optical double resonance of NO2 in the region of 612–614 nm: The role of 2A1 vibronic levels as dark and perturbing state

An optical–optical double resonance (OODR) technique has been applied to the rotational analysis and vibronic assignment of NO2 absorption band in the region of 612–614 nm. The two step excitation through 2 2B2←2B2←X 2A1 has allowed us to determine rotational quantum numbers (NKa,Kc) for 73 eigenstates with B2 vibronic symmetry, lying at 16 306–16 465 cm−1 above the ground state. Although they are severely perturbed and irregular in the rotational structure and spin doubling, we can classify the rovibronic levels as four stacks; two Ka=0 stacks with subband origins of 16 306.2 and 16 321.0 cm−1, and two Ka=1 stacks with origins of 16 312.5 and 16 326.0 cm−1. A near‐prolate asymmetric top approximation is used to obtain the term values and rotational constants. Extraordinary large DN measured for 2B2 vibronic levels can be understood by well‐known, strong vibronic coupling between A 2B2 and highly excited vibrational levels of X 2A1. Among a number of perturbations observed, the spin–orbit (and/or orbit...

Coherent phase control of the product branching ratio in the photodissociation of dimethylsulfide

Coherent phase control of the photodissociation reaction of the dimethylsulfide has been achieved by means of quantum-mechanical interference between one- and three-photon transitions. Dimethylsulfide was irradiated by fundamental and frequency-tripled outputs of a visible laser (600.5-602.5 nm), simultaneously to yield CH3S+ and CH3SCH2+ fragment ions. The branching ratio of the two product channels could be modulated with variation of the phase difference between the light fields. This accounted for the difference between the molecular phases of the two product channels. The phase lag was observed to have a maximum value of 8 degrees at 601.5 nm. This is the first result of a selective bond breaking in a polyatomic molecule by the coherent phase control.

Experimental study of spontaneous ignition limit of oxygen-lean silane mixtures

Abstract The spontaneous ignition of a premixed silaneoxygennitrogen system has been investigated under a variety of conditions. It has been found that the autoignition temperatures are lower than room temperature if the oxygen concentration is extremely low. The spontaneous ignition of silane results from the extremely oxygen-lean mixtures instantaneously produced when silane or silane mixture is poured into the air.

Infrared depletion spectroscopy of aniline–acetonitrile cation and aniline–acetonitrile–water cation clusters

Abstract The vibrational spectra of the aniline–acetonitrile+ and the aniline–acetonitrile–water+ cluster cations have been measured by the infrared depletion spectroscopy in the frequency region of NH and OH stretching vibrations. One absorption band was observed at 3437 cm −1 in the infrared spectrum of the aniline–acetonitrile+ cluster cation, and was assigned to the NH stretching vibration of free NH of aniline. As for the aniline–water–acetonitrile+ cluster cation, three absorptions were observed at 3722, 3634 and 3247 cm −1 , which were assigned to the anti-symmetric stretching and symmetric stretching vibrations of OH of water and the stretching vibrations of NH bond interacting with water, respectively. In the analysis of the vibrational spectrum, the structure of aniline–acetonitrile–water+ cluster cation has been determined to be the hydrogen bonded structure between the hydrogen atoms of the NH2 group of aniline cation and the nitrogen atom in the CN group of acetonitrile and the oxygen atom of water. The predissociation of the aniline–acetonitrile–water+ cluster cation have been found to give only one product channel dissociating into aniline–acetonitrile+ and water.

Competition between two-photon-resonant three-photon ionization and four-wave mixing in Xe

Competitive inhibition of a resonance enhanced multiphoton ionization process by a resonant four-wave mixing has been observed in Xe atoms. When an intense IR (1064 nm) laser was applied to a sample of Xe which was also being irradiated by a UV laser tuned to the two-photon absorption line of Xe, the two-photon-resonant three-photon ionization signals decreased with increasing IR laser power. This phenomenon is dependent on the resonant states of Xe and the polarization of the two laser beams. Three 6s excited states [5/2]{sub 2}, [3/2]{sub 2}, and [1/2]{sub 0} were examined. At the [1/2]{sub 0} resonant state, the ion signals were not decreased but slightly increased with the increase of the IR laser power. No suppression of the ion signal was observed at the [5/2]{sub 2} resonant state, when the polarization directions of the lasers were perpendicular to each other. The result of the polarization dependence reflects the selection rules of four-wave mixing. A simple rate equation analysis including the contribution of two-photon ionization from the [1/2]{sub 0} state by the IR laser well represents the IR laser-power dependence of the ion signal.

Optical–Optical Double Resonance Spectroscopy of NO2 in the 590.1 nm Region

Optical–optical double resonance (OODR) spectroscopy has been applied to the rotational and vibronic analysis of the thirty nine eigenstates of NO2 existing in the energy region of 16,980–17,124 cm-1 above the ground state. These excited states are concluded to be the mixed states of NO2 generated by spin-orbit and/or orbital-rotation interaction between the B2 and A1 vibronic levels. The mixing mechanism of the excited states is discussed in terms of available information on the visible excited states of NO2.