Ellipticity dependent symmetric break of doubly ionized acetylene in strong laser fields

We experimentally investigate symmetric dissociative double ionization of acetylene in femtosecond laser pulses of various ellipticities. Two dissociative ionization pathways with kinetic energy release of 4.8 and 6.0 eV, denoted as the low- and high-E_N pathways, are observed in the spectrum of the ejected fragment ions. The relative yield of the high-E _N gradually increases as compared to the low-E _N when the polarization of the driving laser field is adjusted from linear to circular with increasing ellipticity. The low and high-E _N fragment ions exhibit distinct angular distributions for various field ellipticities. It is attributed to the releasing of electrons from orbitals of different symmetries in producing the low- and high-E _N pathways.