Knowledge Bank

Litterature and new data concerning the $A~-X~$ band system in $C2H2,C2D2$ and $C2HD$ are put together in order to derive information on the $A~$ elctronic state in acetylene. Full sets of vibrational frequencies are determined for the three isotopomers (a). The last original rotational sets of constants characterizing vibrational levels of this state will be also presented. The geometrical structure $(r0)$ is calculated from the results of the rotational analysis. this latter information will be combined with intensity calculations to discuss the axis-switching phenomenon in acetylene. (a) in collaboration with J. Vander Auwera, C. Hamilton, J.L. Kinsey and R.W. Field.