Vibrational predissociation in argon complexes of 3hyphen;aminohyphen;shyphen;tetrazine and 3hyphen;aminohyphen;6hyphen;methylhyphen;shyphen;tetrazine: Evidence for extreme modehyphen;selectivity

摘要

We have investigated the vibrational predissociation of argon complexes of 3hyphen;aminohyphen;shyphen;tetrazine (AT) and 3hyphen;aminohyphen;6hyphen;methylhyphen;shyphen;tetrazine (AMT). Twelve vibrational levels of complexes of the form ATndash;Arn, wheren=1, 2, and 3, were examined. The dissociation rate of the binary ATndash;Ar complex varied from 3times;106sminus;1to 4times;108sminus;1depending on the initially excited mode, with the fastest rate corresponding to the lowest energy vibration. Even levels with vibrational energies over five times that needed to break the van der Waals bond still showed significant amounts of fluorescence from the unfragmented complex. Photodissociation of the ATndash;Ar2complex can yield two different dissociation products, AT and ATndash;Ar. The ratio of these photoproducts varied greatly among different vibrational modes. The 16b2level of ATndash;Ar2at +462 cmminus;1gives primarily the AT photoproduct, while the 16a2level at +505 cmminus;1gives exclusively the ATndash;Ar photoproduct. The two levels of ATndash;Ar3which were studied both appear to show only partial fragmentation. We examined the basic spectroscopy of AMT using vibrationally resolved fluorescence excitation spectroscopy, and assigned a number of vibrational levels in both the ground and excited states. We then used this information to measure the branching ratios and dissociation rates for seven vibrational levels of AMTndash;Ar. These vibrational predissociation rates show strong qualitative differences from similar data for tetrazinendash;Ar and aminotetrazinendash;Ar complexes. Finally, these results were compared to similar work on other tetrazine derivatives to attempt to account for this strong modehyphen;selective behavior.