The study of single molecules delivers deep insights into bonding nature and underlying quantum mechanics concerning about controlling chemical reaction. The scanning tunneling microscope (STM) is a versatile and powerful tool for investigating and controlling chemistry of individual molecules on the solid surfaces. The coupling of tunneling electrons to the electronic and vibrational states of the target molecule allows us to realize mode-selective and state-selective chemistry of the individual molecules. I will address three main issues with our experimental and theoretical efforts on investigating energetics at interfaces of a single molecule with metal surface as well as with ultrathin insulating film surfaces.

The first part is assigned to the excitation of vibrational modes to selectively induce particular dynamic motion [1-4] and chemical reaction [4-6] of a single molecule on the metal surfaces. The microscopic mechanism of vibrationally induced molecular motions [2,4] and the selection rules for the single-molecule vibrational spectroscopy [7] are also discussed. The second part focuses on the selective control of reaction pathways by use of long lifetime of vibrationally and electronically excited states of a water molecule on an ultrathin insulating MgO surface grown on Ag(100) surface [8,9].

Finally, optical properties of a single metal-free phthalocyanine (H₂Pc) molecule on the 2-ML thick NaCl film supported by Ag(111) have been also studied by scanning tunneling luminescence spectroscopy [10]. I will discuss about the single molecule reaction of a H₂Pc molecule with tunneling electrons and accompanied optical property changes in a single-molecule luminescence spectra.

References

[1] T. Komeda, Y. Kim, M. Kawai, B.N.J. Persson, H. Ueba, Science 295 (2002) 2055.

[2] Y. Sainoo, Y. Kim, T. Okawa, T. Komeda, H. Shigekawa, M. Kawai, Phys. Rev. Lett. 95 (2005) 246102.

[3] S. Katano, Y. Kim, Y. Kagata, M. Kawai, J. Phys. Chem. C 113 (2009) 19277.

[4] M. Ohara, Y. Kim, S. Yanagisawa, Y. Morikawa, M. Kawai, Phys. Rev. Lett. 100 (2008) 136104.

[5] Y. Kim, T. Komeda, M. Kawai, Phys. Rev. Lett. 89 (2002) 126104.

[6] S. Katano, Y. Kim, M. Hori, M. Trenary, M. Kawai, Science 129 (2007) 1883.

[7] K. Motobayashi, Y. Kim, H. Ueba, M. Kawai, Phys. Rev. Lett. 105 (2010) 076101.

[8] H.-J. Shin, J. Jung, K. Motobayashi, S. Yanagisawa, Y. Morikawa, Y. Kim, M. Kawai, Nature Materials 9 (2010) 442.

[9] J. Jung, H.-J. Shin, Y. Kim, M. Kawai, J. Am. Chem. Soc. 133, 6142 (2011); J. Am. Chem. Soc. 134, 10554 (2012).

[10] H. Imada, M. Imai, T.K. Tomoko, and Y. Kim, to be submitted.