Molecular beam stimulated emission pumping spectroscopy of propynal

Abstract

Stimulated emission pumping (SEP) experiments were performed on propynal (H–C≡C–CHO). The SEP spectra probed the overtones of the pure C=O stretch (ν4) and a combination of the C=O stretch with the C≡C–C bend (ν9). Term energies for J≤8, K≤2 of the vibrations 42, 43, 44, 45, 4391 as well as two unidentified perturbing vibrational states were obtained. The SEP spectra show simple rotational structure that is assignable by means of a near prolate asymmetric top model. Rotational constants were obtained for all the vibrational states measured. Spectroscopic perturbations are observed for ν4=2,4,5 as either anomalous rotational constants, anomalous energy level shifts, or as extra spectral transitions. Complex state mixing is not observed at the current spectroscopic resolution (0.04 cm−1) even though vibrational state densities as high as 400 states per cm−1 were probed. The propynal SEP results are compared to other SEP experiments on aldehyde containing molecules and inferences are made.