15min:

RÉMY JOST, PATRICK DUPRÉ, PATRICE THEULÉ, ANTOINE DELON, Grenoble High Magnetic Field Laboratory, CNRS-MPI, BP 166, 25 Rue des Martyrs 38042 GRENOBLE, Cedex 9, France; MARCEL JACON, GSMA, UFR Sciences, BP 1037, 51687 REIMS Cedex 2, France.

We present a comparison between experimental results (vibronic energies, absorption and LIDFS intensity ratios, rotational constants) and ab-initio calculations (diabatic and adiabatic energies, vibronic matrix elements). The three main inputs required in the analysis of the \( X ²A₁-A ²B₂ \) conical intersection are: i) the diabatic levels of the \( X ²A₁ \) state (\textsli.e., the complete set of approximatively 200 low lying levels of the \( X ²A₁ \) observed by LIDFS), ii) the diabatic levels of the \( A ²B₂ \) state (they are approximately predicted by the ab-initio calculations), iii) the matrix elements of the vibronic interaction, \( V₁₂ \), between the \( X ²A₁ \) and \( A ²B₂ \) electronic states. The validity of the simplified form proposed for \( V₁₂ \), namely ``\( Q₃ \)'', will be discussed. The comparison allows to assign some observed vibronic levels, which in return can be used to improve some parameters of the initial ab-initio PESurfaces. Up to now, our analysis is limited to the four lowest polyads of the \( A ²B₂ \) state ranging from \( 9700 \mathrmcm^-1 \) to \( 12300 \mathrmcm^-1. \) At higher energy the interactions are stronger, leading to vibronic chaos above \( 17000 \mathrmcm^-1. \)