Ultrabroad supercontinuum is generated when ultrashort laser pulses are injected into a photonic crystal fiber (PCF). Owing to the low threshold for the supercontinuum generation, the experimental setups have been significantly simplified by PCFs. We have applied the PCF-based supercontinuum light source to develop unique coherent Raman spectrometers. In the present paper, I would introduce two coherent anti-Stokes Raman scattering (CARS) systems, namely femtosecond CARS spectroscopy and ultrabroadband multiplex CARS microspectroscopy, both of which require only a single Ti:sapphire oscillator as a laser source. The former allows us to investigate vibrational dynamics in real time, while the latter provides molecular specific multi-color images for biological samples with high speed. In particular, we have successfully visualized the mitosis process of living fission yeast cells at the molecular level.
We studied single gold nanoparticles and aggregates by linear and non-linear optical methods combined with near-field optical microscopy. Near-field images of gold nanorods obtained show peculiar spatial patterns, and are strongly dependent on wavelength observed. The images are attributed to spatial characteristics of plasmon modes (wavefunctions), and are consistent with theoretical simulations. We also studied spatial distributions of optical fields by using near-field two-photon-induced photoluminescence and Raman imaging techniques. We revealed that optical fields are highly confined at interstitial sites in dimers of spherical gold nanospheres, and such an amplified electromagnetic field is one of the most important origins in single molecular sensitivity surface enhanced Raman scattering.
Supersonically cooled, π-conjugated molecular cluster anions are efficiently produced up to more than 100 constituent molecules and their electronic states are size-selectively investigated using anion photoelectron spectroscopy. Homogeneous anionic clusters of anthracene, (anthracene)n- (n = 1-100), are presented herein as one of noteworthy results among those studies. The coexistence of two types of anionic isomers is found over a broad range in size: isomers I and II-1 (n = 4-30) or isomers I and II-2 (n ≥ 40). Size-dependent energetics, vibrational features, and temperature variations of photoelectron spectra for each isomer allow us to infer their structural motifs, electron accommodation modes, and formation mechanisms. Such improved knowledge increases our comprehension about size effect on cooperative nature between electronic states and structures of π-conjugated molecular aggregates at a molecular-level.
With the advent of the Kraetschmer-Huffman historical breakthrough on the macroscopic synthesis of C60 in the late summer of 1990, I decided to stop all my research so far doing in the area of spectroscopy of gas-phase molecular clusters. Since then, my Odyssey in and quest for the so-called nano-carbons started. Thanks to the brand-new and wonderful world of fullerenes, metallofullerenes, carbon nanotubes and nano-peapods, I have been able to entertain (and still entertaining !) “the pleasure of finding things out” as Richard Feynman once put it in an interview by a BBC television program in 1981. I believe that as long as one has big dreams and lay groundwork for the dreams one will achieve them. My quest for nano-carbons is still on the way.
A history of the development of molecular conductors is briefly summarized. As a typical example of recently developed organic conductors exhibiting electro-magnetic properties, the magnetic organic superconductors developed by author's group are presented. The metallization of single-component molecular crystals is also discussed from the viewpoint of the molecularity and metallicity.
We review a recent development in a rigorous non-Born-Oppenheimer method, i.e., nuclear orbital plus molecular orbital (NOMO) method, which determines the nuclear and electronic wave functions simultaneously. The NOMO theory is an exact theory for the non-BO problem in principle; for example, full-configuration interaction formulation for a complete configuration space. Hartree-Fock equations for nuclear orbitals and molecular orbitals are derived for practical calculations. The usage of Gaussian basis functions for nuclear orbitals is discussed. We formulate the elimination of translational and rotational contaminations in the NOMO method. Furthermore, many-body effects such as nucleus-nucleus, nucleus-electron, and electron-electron correlations are investigated by applying the second-order Møller-Plesset perturbation theory to the NOMO method. The excited-state theories such as configuration interaction and generator coordinate method are examined to describe not only electronic but also vibrational excited states.
Nonadiabatic transitions play crucial roles in chemical dynamics not only to comprehend the dynamics but also to develop and control molecular functions. The Zhu-Nakamura theory which overcomes the defects of the Landau-Zener theory can be usefully utilized for these purposes. Based on our recent achievements the following subjects are discussed: (i) new methodologies to treat nonadiabatic chemical dynamics of many degrees of freedom, (ii) new ideas to control various chemical dynamics by lasers, and (iii) development and control of molecular functions by manipulating nonadiabatic transitions.
Two or three-dimensional potential energy surfaces have been determined for open-shell radical complexes, Rare-gas-OH and SH, using. a free-rotor model considering all the couplings between various anagular momenta existing in the radical complexes. Hamiltonian matrices upto 48,000 dimensions have bee numerically diagonalized to obtain ro-vibronic energy levels within accuracies of microwave spectroscopy. All the observed data, including those of isotopomers, OD or SD, and those of excited vibrational states of the OH monomer for the case of Ar-OH, have been successfully fitted, yielding fairly precise 2 or 3-dimensional potential energy surfaces. It is expected that the method could be extended to more complex systems.
Chemistry has grown up based on a huge pile of experimental evidence on chemical substances and guided by a number of empirical rules. In this modern age, by the aid of quantum and statistical mechanics and with relativistic theory many of experimental facts can be calculated and predicted to a considerable accuracy. However, a majority of chemists do not realize the essence and importance of basic theories and mathematics in chemistry, but rather they still attach to old fashioned empirical rules without knowing their logical proof or limitation. The present author points out the important role of mathematical chemistry which is not only unveiling these prevailing dogmas but also giving sound mathematical foundation to modern theories. He also warns of the present status of chemical education in Japan where mathematicsphobia.and sciencephobia are prevailing.