Infrared overtone spectroscopy of adsorbed hydrogen in MOF-5

Overtone spectroscopy is used to observe the rovibrational spectra of the hydrogen isotopologues H-2, HD, and D-2 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 H-2 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 Q(2)(0) pure vibrational mode is found to be anomalously large, most likely arising through mode coupling to the MOF-5 framework. (C) 2014 Elsevier Inc. All rights reserved.