ELECTRONIC STRUCTURE AND PHOTODISSOCIATION OF $HgCl_{2}$
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Date
1979
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Ohio State University
Abstract
Ab initio configuration interaction calculations using relativistic effective core potentials and flexible basis sets have been used to study and assign the electronic spectrum of $HgCl_{2}$. The lowest dipole-allowed transition is $1^{I}\Sigma^{+} \rightarrow 1^{1}\Pi_{u}$, which corresponds to a charge transfer from a $C1^{3}p\Pi$ orbital to the Hg 6s-like orbital. Upon dissociation this state correlates with $HgCl(A^{2}\Pi) + Cl(^{2}P)$. The second stronger dipole-allowed transition is $1^{1}\Sigma^{+}_{g} + 1^{1}\Sigma^{+}_{u}$, which corresponds to a charge transfer from a Cl $^{3}p\Pi$ orbital to a Hg $^{6}p\Pi$ orbital. The $1^{1}\Sigma^{+}_{u}$ state will dissociate to $HgCl(B^{2}\Sigma^{+}) + Cl(^{2}P)$. This explains why excitation of the second band ($\sim 180$ nm) in $HgCl_{2}$ leads to $fluorescence^{2}$ or $lasing^{3}$ on the $B^{2}\Sigma^{+} \rightarrow X^{2}\Sigma^{+}$ transition in HgCl. The effect of bending on the energies of the excited $1^{1}\Pi_{u}$ and $l^{l}\Sigma^{+}_{u}$ states in $HgCl_{2}$ is investigated and the implications for the photodissociation process are considered.
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$^{1}$ L. R. Kahn. P. J. Hay and R. D. Cowan, J. Chem. Phys. 68, 2386 (1978). $^{2}$ K. Wieland, Z. Phys, 77, 157 (1932). $^{3}$ J. G. Eden, Appl. Phys. Lett. 33, 495 (1978).
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