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 inito potential energy surfaces for an NO2 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.