Overlap parameters of ${\mathrm{H}}_2$-${\mathrm{H}}_2$ molecular pairs from the absorption spectra of the collision-induced fundamental band of ${\mathrm{H}}_2$

The collision-induced fundamental infrared absorption band of ${\mathrm{H}}_2$ in the pure gas at 77, 196, and 298 K was recorded for a number of gas densities up to 60 amagat. An analysis of the absorption profiles was performed by assuming appropriate line shapes, and the characteristic half-width parameters ${\delta }_d$ and ${\delta }_c$ of the short-range overlap-induced transitions and ${\delta }_q$ (and ${{\delta }_q}^{\prime }$) of the long-range quadrupole-induced transitions were determined. From this analysis the contributions to the intensity of the band from the overlap and quadrupolar interactions were separated. For the ${\mathrm{H}}_2$-${\mathrm{H}}_2$ molecular pairs, the overlap parameters, $\lambda$ and $\rho$, which give, respectively, the magnitude and range of the overlap dipole moment, and $\mu \left(\sigma \right)$, the overlap-induced dipole moment at the Lennard-Jones intermolecular diameter $\sigma$, were determined by obtaining the best fit of the calculated overlap parts of the binary absorption coefficients as a function of temperature to the experimental values. The values of the overlap parameters obtained are $\lambda =4.53\mathrm{}\times {10}^{-3\mathrm{}}$, $\rho =0.23\mathrm{}$ Å, and $\mu \left(\sigma \right)=2.5\mathrm{}\times {10}^{-2\mathrm{}}e{a}_0$.