The excitation spectrum of cyanoacetylene (HC3N) and emission from C3N fragments

We have measured an ultraviolet action spectrum following excitation of cyanoacetylene between 212 and 264 nm. The low yield emission, principally to the red of 290 nm, is shown to be the product of multiphoton processes. Below 230 nm, secondary photolysis of metastable HC3N∗ yields electronically excited C3N. Metastable HC3N∗ can be monitored by separately exciting the metastables at 193 nm and then photodissociatively exciting them at 220 nm. The process leading to emission above 240 nm is more complex involving formation of a stable intermediate followed by its photodissociative excitation.