COMPARISON BETWEEN THEORY AND EXPERIMENT FOR EXCITED STATES OF MOLECULAR HYDROGEN
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Date
1984
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Ohio State University
Abstract
The excited $^{1}\Sigma_{g}^{+}$ states of the $H_{3}$ molecule are affected by strong nonadiabatic coupling. The interaction of the doubly excited $i \sigma_{u}{^{2}}$ configuration with Rydberg configurations $\sigma_{g}$ gives rise to the double-minimum electronic energy curves of the states $EF (2s\sigma_{g}2{^{1}}\sigma_{g}^{+}),GK (3d\sigma_{g}, 3{^{1}}\sigma_{g}^{+})$, and to the higher lying curves of the states $i{^{1}}\sigma_{g}^{+}(i=4,5,\ldots)$ which continue the $ns\sigma$ and $nd\sigma$ series. The vibrations of all of these adiabatic states $i^{1}\Sigma_{g}^{+}$ are mutually coupled via the operators $<i|d^{2}/dR^{2}|j>+2<i|d/dR$ which have been computed by Wolniewicz using ab-initio wavefunctions $(i,j) = (2,3)$ and (3,4), and by Quadrelli using an approximate diabatic model for the entire $nd\sigma$ and $nd\sigma$ Rydberg series interacting with $1\sigma u^{2}$ The discrepancies between the nonadiabatic ab-initio results and experimetal term values increase with vibrational excitation energy from $2cm^{-1}$ for $EF(v=0)$ to $50cm^{-1}$ for $GK(v=5)$ and they can be apportioned approximately to (a) convergence errors of the adiabatic potential energy curves (up to $\simeq 20cm^{-1}$) and (b) nonadiabatic shifts caused by the higher states $i > 4$ (up to $\simeq 30 cm^{-1}$). This has been investigated with the aid of Quadrelli's model as well as by comparing the ab-initio results for $H_{2}$ and $D_{2}$. For the $v=0$ level of the EF state the nonadiabatic energy shift is smaller than $0.1cm^{-1}$; the $2cm^{-1}$; error of the adiabatic calculation is of magnitude comparable to ab-initio results on other excited states of $H_{2}$.
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Author Institution: Physical Chemistry Laboratory