Experimental results are presented which show UV excitation to metastable states of C2H2 above and below the dissociation limit. A strong S-1-T-3 interaction, located close in energy to the S(1)3 nu(3) (trans-bend) vibrational level is detected. A ''gateway mediated intersystem crossing'' singlet-tripler coupling mechanism explains the results. (C) 1997 American Institute of Physics.