Vibrational spectroscopic evidence for (NO)3 formation on Cu(111)

The formation of (NO)3 on Cu(111) was recently reported based on scanning tunneling microscopy observations [A. Shiotari et al., J. Chem. Phys. 141, 134705 (2014)]. We herein report studies into this system using electron energy loss spectroscopy and verify the above findings through vibrational analysis. For the surface covered with mixed isotopes of N(16)O and N(18)O, we observed four peaks corresponding to N-O stretching vibrations, which were ascribed to the four isotopic combinations of the trimer. Dynamic coupling within the trimer was evaluated from model calculations of the coupled oscillators. Furthermore, we observed hindered rotation and translation modes in the dipole scattering regime, suggesting that the molecular axis is tilted from the surface normal. These results provide spectroscopic support for the formation of (NO)3 on Cu(111).