Observation of the C2H radical using (1 + 2) REMPI via the B̃2A′←X̃2Σ+ transition

We report the detection of the ethynyl (C2H) radical by (1 + 2) REMPI on the B̃2A′(T,Ka=0,1,2)←X̃2Σ+(0,31,0) transition. One parallel, B̃2A′(T,Ka=1)←X̃2Σ+(0,31,0) with EeV=37,946cm-1, and two perpendicular transitions, B̃2A′(T,Ka=0)←X̃2Σ+(0,31,0) with EeV=37,927cm-1 and B̃2A′(T,Ka=2)←X̃2Σ+(0,31,0) with EeV=38,002cm-1, are observed. The C2H radical was generated by the photodissociation of C2H2 at 193 nm. By employing REMPI spectroscopy, we also studied the collisional induced rotational relaxation of C2H and measured rotational relaxation rate constants for this radical. The measured rotational relaxation rate constants for several values of J″ are (0.08-0.26)×10-9cm3molec-1s-1 and (0.75-1.92)×10-9cm3molec-1s-1 for nitrogen buffer gas and acetylene, respectively.