BANDS OF THE 2400 \AA SYSTEM OF ACETYLENE.

Abstract

Detailed assignments of the longer wavelength bands of the $2400 \AA$ absorption system $A^{-1}A_{\mu}(C_{2h})-\tilde{X}^{1}\Sigma^{+}_{g}(D_{\omega h})$ of acetylens $(C_{2}H_{2})$ have been performed, including revisions of some subband assignments. The wavenumbers of the lines of the stronger bands have been fitted simultaneously employing a linear molecule Hamiltonian for the lower electronic state, with inclusion of $\ell$-doubling and $\ell$-resonance effecta in the lavels of the $\pi_{g}$ vibration $\upsilon_{4}$ for $\upsilon_{\Delta} \epsilon 4$, and an asymmetric top Hamiltonian with centrifugal distortion for the upper electronic state. The relative intensities of different subbands, including the effects of axis-switching, will be discussed. The observed vibrational levels of the upper state below $2500 cm^{-1}$ are fairly regular, Estimates of the unobserved fundamentals will be presented. The analysis will be continued to higher vibrational levels, where quasilinear effects should become important.