Infrared overtone spectroscopy of adsorbed hydrogen in MOF-5

- IR overtone spectroscopy is shown to aid the identification of obscured modes.
- The (ro)vibrational modes of D2 and HD adsorbed in MOF-5 are observed.
- Overtone bands of H2 at primary adsorption site are greatly enhanced.
- Q2(0) is significantly enhanced compared to other overtone modes.
- Enhancement is attributed to coupling to a MOF carboxylate stretch mode.

Overtone spectroscopy is used to observe the rovibrational spectra of the hydrogen isotopologues H2, HD, and D2 adsorbed in the metal-organic framework known as MOF-5. It is shown that the overtone spectrum facilitates the identification of hydrogen modes which are obscured in the fundamental region by the presence of MOF-5 features. Further, the overtone spectrum of H2 at the primary adsorption site is greatly enhanced relative to other sites, and thus ambiguities about feature assignment can be avoided. The frequency (wavenumber) of the overtone modes are in good agreement with a Buckingham perturbative model while the relative intensity of the Q2(0) pure vibrational mode is found to be anomalously large, most likely arising through mode coupling to the MOF-5 framework.

98