Stimulated Emission Pumping(SEP) Spectroscopy of Propynal: An Example of “Sparse” IVR at High Vibrational State Density

SEP spectra were recorded for the overtones of the C=O stretch(ν4) up to ν4=5 and one combination band with three quanta of C=O stretch and one quanta of in plane C≡C−C bend(ν9). The experiments were performed in a molecular beam, using two excimer pumped dye lasers with etalons for the PUMP and DUMP steps giving an experimental resolution of 0.04 cm-1. The resulting SEP spectra are simple and assignable to a near prolate asymmetric top. Anharmonic perturbations manifest themselves in the SEP spectra for ν4=4 and 5 as extra transitions. Anharmonic perturbations from unobserved levels appear in the rotational constants for ν4=2 and 3.