Knowledge Bank

While the fundamental bands of ethylene have been studied at high resolution, most of the combination bands have not been recorded. In this study, we have recorded the $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}$C$2$H$4$ bands in the 1820 to 2300 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region which consists of a myriad of weak combination bands. Over 10,000 lines were measured. The strongest of these bands are the A-type band, \nu$7$+\nu$8$ , centered at 1889 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, the A-type band, \nu$6$+\nu$1$$0$ , at 2048 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, and the B-type band, \nu$3$+\nu$1$_0$,at2173cm$^{-1}$.Inaddition,therearenumerouslinesfrommuchweakerbands.AllthebandsobservedareperturbedbyCoriolisinteractions,and,atthispoint,weareattemptingtofitallthelinestowithinexperimentalerrorusinganHamiltonianmatrixincludingeigthvibrationalstatesamongwhichfouraredarkstates.Themoststrikingresonanceisthatofthe\nu$_7$+\nu$_8$ band whose energy levels are crossed by the very much weaker \nu$4$+\nu$8$ band where the intensities of the K=7 lines are enhanced due to mixing with the stronger band.