Dynamical symmetry breaking in the 4νCH rovibrational manifold of acetylene

Time-resolved, fluorescence-detected infrared-ultraviolet double resonance spectroscopy of acetylene in the 12700 cm−1 ‘4νCH’ rovibrational manifold reveals unusual symmetry-breaking energy transfer, induced (at least in part) by collisions. This takes the form of odd-numbered changes of the rotational quantum number J, despite the fact that intramolecular transfer between the ortho and para nuclear-spin modifications of such a molecule is usually forbidden.