“…As part of this family, directly observed infrared absorption spectra have yielded an extensive vibrational-spectroscopic database − ,,− and have enabled a global fit of the vibrational energy pattern to available spectroscopic data up to ∼19 000 cm -1 in terms of the polyad/cluster model. Likewise, measurement of dispersed rovibronic LIF from the S 1 (trans-bent à 1 A u ) electronic state, entailing laser excitation of a single low- J Ã−X̃ transition (either under gas-phase conditions that allow collisional relaxation or collision-free in a molecular beam) combined with elegant numerical pattern-recognition methods, also provide an alternative direct spectroscopic view of vibrational states of C 2 H 2 at high energies (typically 6 000−20 000 cm -1 ). ,, A complementary spectroscopic technique, also relatively direct, is stimulated emission pumping (SEP), which has been applied extensively to high-energy vibrational states of C 2 H 2 . 60d,, Spectroscopic databases derived as above include many important homogeneous vibrational perturbations (e.g., anharmonic mixing and vibrational l -doubling) that can be characterized in the low- J limit. However, local J -dependent perturbations (e.g., rotational l -resonance and Coriolis coupling) tend to be treated on a case-by-case basis. ,,,, …”