Assignment of rovibrational transitions of propyne in the region of 2934-2952 cm^-1 measured by two-color IR-vacuum ultraviolet laser photoion-photoelectron methods

The infrared (IR) spectrum of propyne in the region of 2934-2952 cm^-1 has been recorded by the IR-vacuum ultraviolet (VUV)-photoion method. The spectrum is shown to consist of two near-resonant, but noncoupled vibrational bands: the v₂ symmetric methyl C-H stretching vibrational band and a combination vibrational band v_cs. The previously unobserved Q line of the v_cs band is observed. The rotational transition lines of the v₂=1 band produces IR-VUV-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) signal at the C₃H₄⁺ (v₂⁺=1) photoionization threshold. The rotational transition lines associated with the v_cs band do not produce IR-VUV-PFI-PE signal. Rotational transition lines of both vibrational bands are assigned and simulated; and ab initio calculations further confirm the assignment. © 2007 American Institute of Physics.