Knowledge Bank

We have recorded the high resolution spectrum of several overtone bands in diacetylene and diacetylene-$d1$ using optothermal detection of a collimated molecular beam. The first overtone of the acetylenic CH stretches in these two molecules were recorded by single resonance using $1.5\mu m$ color center laser. The second overtone spectra were taken using sequential infrared/infrared double resonance with two color center lasers. In diacetylene we also recorded a combination band. Which in the local mode picture is equilvalent to putting two quanta in one acetylenic CH strength and one quanta at the other end of the molecule. Comparison of this spectrum with the spectrum of three quanta in the same CH stretch confirms earlier observations that, if the molecule is not too small, ``extreme motion” states are mor perturbed than combination $bands1$. The interesting and varied dynamics found in these two molecule cannot be attributed to such thing as exciting different types of bonds, internal rotation or isomerization, but instead comes purely from the anharmonic coupling present in each molecule.