Energy conversion in van der Waals complexes of s-tetrazine and argon

Abstract

The van der Waals complex T·Ar has been prepared by expanding argon seeded with s-tetrazine through a nozzle. The complex dissociates when excited to single vibronic levels of the S₁(¹B_3u) state of tetrazine. Information about both the vibrational state distribution of the dissociation fragment T and vibrational relaxation which takes place in the complex has been obtained from spectrally resolved and time-resolved fluorescence. The relative yields of relaxation and dissociation processes depend upon the excess vibrational energy ε_w absorbed by the van der Waals modes. The magnitude of ε_w was varied using different sequence transitions of the van der Waals modes, by tuning the laser successively to different wavelengths within the contour of a particular absorption band. The observed effects can be interpreted qualitatively in terms of the momentum-gap law. The dissociation of the text-decoration:overline6a¹ state of T·Ar proceeds via two consecutive steps. Lower and upper limits to the dissociation energy D^′ ₀(of the text-decoration:overline6a¹ state) are 276 and 448 cm^–1. Energy transfer from the 16a mode as well as from the 16b mode to the van der Waals bond gives rise to dissociation of the complex. The dissociation rates are of the order of 10⁹ s^–1 and they are dependent on ε_w.