Knowledge Bank

With an absorption path length of $\sim 13m$ in $H2$-rare gas mixtures above the boiling point of the rare gas, the Q, S(0) and S(1) components of the pressure-induced fundamental infrared band of $H2$ exhibit a fine structure which can be interpreted as transitions between bound states of $H2$-rare gas complexes. The fine structure is best defined for the S(0) transition in mixtures with pure parahydrogen. The pattern consists of well-resolved T and N branches, $\Delta l=\pm 3$, where l is the rotational quantum number of the complex, and two broad central components with partially resolved structures. The complexes with Ar, Kr and Xe show 7, 9 and 11 bound states, respectively, and the spacings of the T and N lines can be used to calculate effective rotational constants for the complexes. Studies of the temperature dependence of the complex formation will be discussed.