(1+1’) REMPI of Acetylene in a Heated Molecular Beam

We present a 1 + 1′ resonance-enhanced multiphoton ionization (REMPI) scheme for acetylene via the linear G̃ 4sσ 1Πu Rydberg state, offering partial rotational resolution and the possibility to detect excitation in both the cis- and transbending modes. The resonant transition to the G̃ state is driven by a vacuum ultraviolet (VUV) photon, generated by resonant fourwave mixing (FWM) in krypton. Ionization from the short-lived G̃ state then occurs quickly, driven by the high intensity of the residual light from the FWM process. We have observed nine bands in the region between 79200 cm−1 and 80500 cm−1 in C2H2 and C2D2. We compare our results with published spectra in this region and suggest alternative assignments for some of the Renner−Teller split bands. Similar REMPI schemes should be applicable to other small molecules with picosecond lifetime Rydberg states. (Abstract from J. Phys. Chem. A, 2016, 120, 27, 5399-5407)