Current Research and Research Interests

Current research focuses on high intensity laser chemistry, more specifically, ionization and fragmentation, and Coulomb explosion of organic molecules induced by femtosecond laser pulses. Multiphoton reactions via hot molecules formed by internal conversion using a VUV laser is another subject of interests.

1. High-Intensity Laser Chemistry

New research fields have opened related to the interaction between molecules and high-intensity optical fields, where the laser intensity ranges from 10¹²~10¹⁷ W cm^-2. For large molecules, a parent ion with little fragmentation has been found to form in an intensity region lower than 10¹⁵ W cm^-2. The intact ion formation can be used for femtosecond laser mass spectrometry. In an intensity region higher than 10¹⁶ W cm^-2, electrons are stripped from molecules by optical field ionization and the highly charged ions reach a Coulomb explosion. Coulomb explosions of benzene and C60 have been demonstrated and the mechanism can be analyzed by molecular dynamic simulation .

1.1 Parent and Fragment Ion Formations of Organic Molecules on Irradiation with an Intense Femtosecond Laser Pulse

[Chem. Phys. Lett. 342,563(2001).].

Figure 1. Mass spectra of 1,3-cyclohexadiene (1,3-CHD) and 1,4-cyclohexadiene (1,4-CHD) observed at 800 nm with a 130 fs pulse width at 0.7x10¹⁴ Wcm^-2. The parent ions are denoted by P⁺, and the doubly charged parent ions by P²⁺. 1,3-CHD⁺ is not in resonance with the laser wavelength and results in a high yield of parent ion formation, while 1,4-CHD⁺ is resonant and results in fragmentation.

1.2 Coulomb Explosion of Organic Molecules on Irradiation with an Intense Femtosecond Laser Pulse

[J. Chem. Phys. 112, 5012(2000); Chem. Phys. Lett. 317, 609(2000).] .

Figure 2. MD simulations of Coulomb explosions of C₆₀ and benzene. C₆₀ will be ionized to C₆₀ ⁿ⁺(n >100), C₆H₆^m+(m >20) and explosions are reproduced.

1.3 Detection of dioxins
The phenomena of parent ion formations in intense femtosecond laser fields is going to be applied for detection of dioxins. This group collaborates with Institute for Laser Technology and Institute of Laser engineering, Osaka University.

2. VUV Laser Chemistry
-Formation of Hot Molecules and their Reactions in the Gas Phase-
[J. Phys. Chem. 93,7763(1989); Bull. Chem. Soc. Jpn 74,579(2001).] .

Figure 3 Two-photon reaction via hot benzene produce 1,3-hexadiene-5-yne as a dominant photoproduct. The corresponding vibrational temperature of benzene with two-photon energy of ArF laser light is evaluated to be as high as 5900 K.