\[\left(\frac{{\mathrm{d}}^{2}}{{\mathrm{d}x}^{2}}-\lambda^{2}\left({\mathrm{e}}%
^{-2x}-2{\mathrm{e}}^{-x}\right)-\left(\lambda-\left(n+\tfrac{1}{2}\right)%
\right)^{2}\right)\phi_{n}(x;\lambda)=0.\]