When expansion-cooled acetylene is excited to the n1913n39 vibrational level ~4 quanta of CH-stretch! and then photodissociated at 248.3 nm, the dominant product channel is C 2H~Ã P!. This differs markedly from one-photon 193.3 nm photodissociation, which provides 1200 cm 21 less energy and yields C 2H~X̃ S! as the primary product. Photodissociation at 121.6 nm yields C2H~Ã P! exclusively. © 1995 American Institute of Physics.