Optical conversion of conical intersection to avoided crossing.

We study a mechanism by which a symmetry-allowed conical intersection is converted to an avoided crossing by external breaking of symmetry. With full quantum dynamics on coupled ab initio potential energy surfaces for an NO(2) molecule under a phase controlled far-infrared femtosecond pulse field, we demonstrate that symmetry breaking thus-introduced can indeed convert the conical intersection to an avoided crossing, thereby drastically influencing population transfer through it.