Knowledge Bank

We investigated the evolution of the quantity pt - (V) (product of the vibrational coupled level density by the average coupling) over a range of $4000cm-1$ by using different kinds of experimental methods such as Quantum Beats and Zeeman Anticrossing Spectra (ZAS). Different rovibrational levels (with a few quantum number of rotation) of the first excited electronic state ($A~1Au$) have been studied using a high magnetic fied (up to 8 traIn). The quantum beat analyzis shows, strong perturbations of the interacting triplet state (dark level). These perturbations are attributed to coupling among triplet states (couplings $T1-T2$). A statistical analysis, based principally on Fourier transform calculations, reveals a dependarice of the pseudo-probability law of the anticrossing of the energy levels as a function of the linewidth $(w):p(w)=w6$ with $-1.65\le \varsigma \le =1$. Moreover, we analyze a large anticrossing on the $3\nu 3$ vibrational level, the characteristics of this anticrossing are near the one of a pure singlet-triplet anticrossing: $Vat=3.3(4)GHz,g=1.7(6)$ (g: Lande g factor). By assuming a spin-orbit coupling hamiltonian (and pur singlet-triplet anticrossing), the FT analysis permits to determine the average coupling, the vibrational coupled level density and the product of these 2 quantities. Over the limited energy range that we could explore, that latter clearly shows an explosion expressed by the relation: $Pvit(V)\propto \exp (E(cm-1)/585)$ (where E is the excitation energy). The exponential increase of the quantity $Pvit$ (V) could be due to a triplet ($\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}Bu$ trans-bent $⟶3B2$ as-bent) acetylene linear barrier. Near the top of the barrier (about 45500cm-1) the probability density of vibrational wave function becomes higher in the linear geometry configuration, i.c. the Franck-Condon overlap between the excited $A¯$ state (trans) and the triplet state (cis) becomes higher. The vibrational mode $v3(CCH^$ bending) used for increasing the energy excitation seems play a major past near the top of the isomerization barrier [1,2,3].