Knowledge Bank

High resolution FRIR spectra of $C2H2$ have been obtained from 1800 to $12.000cm-1$. Over 1600 rovibrational transitions belonging to 30 vibrational bands were assigned and analyzed yielding band origins and rotational constants. Band centers were used to calculate various streth/strctch and bend/stretch anharmonic coupling constants. Several resonances of the type between $\nu 3$ and $(\nu 2+\nu 4+\nu 5)0$ were analyzed, and an unperturbed value of $\nu 3$ was determined. This was combined with other data to obtain $\omega m,xm$ and $\lambda$ in the local mode basis. X, k relations were imposed to yield the normal mode constants for $\nu 1$ and $\nu 3$. Treatment of Darling-Dennison resonances in the first two overtone manifolds led to reassignments of previously reported spectra and to the discovery of a Fermiresonance Involving overtones of $\nu 3$ and states containing $\nu 1,\nu 2$, and $2\nu 40$. Calculated rotational constants and intensity data confirm the assignments and Interactions treted in the vibrational analysis. Treatment of these resonances significantly Improves the agreement between calculated and observed transition wavenumbers, providing a coherent picture of acetylene C-H stretch dynamics below $12000cm-1$.