The 13-1A' < X1A' electronic spectra of the 1-but3m-y1 cation (H3CCHCCH) and the H3CCHCCHf -Ne and H CCHCCH+-Ar complexes are measured using resonance enhanced photodissociation over the 245-285 run range, with origin transitions occurring at 35936, 35930, and 35928 cm 1, respectively. Vibronic bands are assigned based onquantumchemical calculations and comParison of the spectra, w those ofthe related linear methyl propargyl (H3C4H2+) and,i.th ProPargyi (H23C H+) cations. The photofragment ions areC.H3' (major)and C4H3+ (minor), with the preference for C2H 3 CZ consistentH3+ with; master equation simulations for a mechanism that involves rapid electronic deactivation and dissociation on the ground state Potential energy surface.