Quenching of vibrationally excited CO(ν=2) molecules by ultra-cold collisions with 4He atoms

The quenching of vibrational excited CO(nu = 2) molecules by He atoms at ultra-low temperature is examined to determine the relative efficiency of the processes that involve the exchange of a double or a single quantum of vibrational energy. We find that at low temperature the double quantum exchange cross-section is orders of magnitude smaller than for the single quantum process. This result is valid for different initial rotational states of the CO mo lecule