High-resolution Absorption Spectra of Acetylene in 142.8-152.3 nm

The absorption spectra of acetylene molecules was measured under jet-cooled conditions in the wavelength range of 142.8-152.3 nm, with a tunable and highly resolved vacuum ultraviolet (VUV) laser generated by two-photon resonant four wave difference frequency mixing processes. Due to the sufficient vibrational and rotational cooling effect of the molecular beam and the higher resolution VUV laser, the observed absorption spectra exhibit more distinct spectral features than the previous works measured at room temperature. The major three vibrational bands are assigned as a C-C symmetry stretching vibrational progress (v(2)=0-2) of the (C) over tilde (1)Pi(u) state of acetylene. The observed shoulder peak at 148.2 nm is assigned to the first overtone band of the trans-bending mode v(4) of the (C) over tilde (1)Pi(u) state of acetylene. Additionally, the two components, 4(2)(0)(mu(1)Pi(u)) and 4(0)(2)(kappa(1)Pi(u)), are suggested to exhibit in the present absorption spectra, due to their Renner-Teller effect and transition selection rule. All band origins and bandwidths are obtained subsequently, and it is found that bandwidths are broadened and lifetimes decrease gradually with the excitation of vibration.