Knowledge Bank

A high-resolution $(0.0018cm-1)$ infrared spectrum has been recorded for the C-type band ($au$) for CH out-of-plane flapping at $934cm-1$ of trans,trans-1,4-difluorobutadiene (ttDFBD). Considerable progress has been made in analyzing the rotational structure of this band despite hot band structure and numerous perturbations. Assigned series extend from $Ka\prime \prime$ of 4 to 28 in the R branch and $Ka\prime \prime =6$ to 30 in the P branch. Pertubations due to Coriolis coupling occur for $Ka\prime =4,11,16,24$, and 28, for which perturbing states are suggested. More than 1150 ground state combination differences have been fitted to a Watson-type Hamiltonian to give $A=1.0507503(7)$, $B=0.0389679(5)$, and $C=0.0375835(4)cm-1$ for the ground state of this near-prolate top, which has $k=-0.9973$. The goal is to obtain a structure for ttDFBD as part of a study of the three isomers of DFBD, in which the cis effect is observed.