  The capability to excite, probe, and manipulate vibrational modes is
essential for understanding and controlling chemical reactions at the molecular
level. Recent advancements in tip-enhanced Raman spectroscopies have enabled
the probing of vibrational fingerprints in a single molecule with
Angstrom-scale spatial resolution. However, achieving controllable excitation
of specific vibrational modes in individual molecules remains challenging.
Here, we demonstrate the selective excitation and probing of vibrational modes
in single deprotonated phthalocyanine molecules utilizing resonance Raman
spectroscopy in a scanning tunneling microscope. Selective excitation is
achieved by finely tuning the excitation wavelength of the laser to be resonant
with the vibronic transitions between the molecular ground electronic state and
the vibrational levels in the excited electronic state, resulting in the
state-selective enhancement of the resonance Raman signal. Our approach sets
the stage for steering chemical transformations in molecules on surfaces by
selective excitation of molecular vibrations.
