  Quantum state-resolved spectroscopy was recently achieved for C60 molecules
when cooled by buffer gas collisions and probed with a midinfrared frequency
comb. This rovibrational quantum state resolution for the largest molecule on
record is facilitated by the remarkable symmetry and rigidity of C60, which
also present new opportunities and challenges to explore energy transfer
between quantum states in this many-atom system. Here we combine state-specific
optical pumping, buffer gas collisions, and ultrasensitive intracavity
nonlinear spectroscopy to initiate and probe the rotation-vibration energy
transfer and relaxation. This approach provides the first detailed
characterization of C60 collisional energy transfer for a variety of collision
partners, and determines the rotational and vibrational inelastic collision
cross sections. These results compare well with our theoretical modeling of the
collisions, and establish a route towards quantum state control of a new class
of unprecedentedly large molecules.
