Threshold ion-pair production spectroscopy of HCN.

The spectroscopic technique of threshold ion-pair production spectroscopy (TIPPS) has been applied to the triatomic molecule HCN. We have recorded the total ion-pair yield and TIPP spectra for the HCN→H++CN- process using coherent vacuum ultraviolet excitation. From the simulation of our high-resolution TIPP spectrum we have precisely measured the HCN ion-pair threshold EIP0 to be 122 244±4 cm-1. This value could be used to determine the bond dissociation energy D0(H-CN) to unprecedented accuracy. Our fitting result also showed that rotationally excited instead of cold CN- fragment is favored as the ion-pair dissociation product in the threshold region. [ABSTRACT FROM AUTHOR]