High-Resolution Spectroscopy and Structure of Osmium Tetroxide. A Benchmark Study on ¹⁹²OsO₄

Abstract

Osmium tetroxide (OsO(4)) is a heavy tetrahedral molecule that constitutes a benchmark for quantum chemistry calculations. Its favorable spin statistics (due to the zero nuclear spin of oxygen atoms) is such that only A(1) and A(2) (T(d) symmetry) rovibrational levels are allowed, leading to a dense but quite easily resolvable spectrum. We reinvestigate here the ν(1)/ν(3) stretching fundamental (940-980 cm(-1)) dyad region and perform new assignments and effective Hamiltonian parameter fits for the main isotopologue ((192)OsO(4)). We also investigate the ν(2)/ν(4) bending fundamental dyad (300-360 cm(-1)) for the first time and perform a preliminary analysis. New experimental data have been obtained at 0.001 cm(-1) resolution using an isotopically pure (192)OsO(4) sample and the Synchrotron SOLEIL light source. Assignments and analyses were performed using SPVIEW and XTDS software, respectively. We provide precise effective Hamiltonian parameters, including the band centers for all of the fundamental levels and rotational constants for the ground state and for all four fundamental levels. We discuss isotopic shifts, estimate the equilibrium rotational constant B(e), and derive a precise value for the equilibrium bond length r(e)(Os-O) = 1.70919(16) Å. We also performed experiments to measure for the first time the IR integrated intensities for the ν(2)/ν(4) bending fundamental dyad. These new data are compared to current ab initio predictions.

High-resolution infrared spectroscopy and analysis of the ν2/ν4 bending dyad of ruthenium tetroxide

“…The general shape (contour, relative intensities) of the dyad was very understandably strongly dependent upon the energy interval between effective band centers and the extent of the Coriolis interaction. Again, since 24 …”

“…As will be seen later, the actual values for and depart only by -5 and +8 % from these starting guesses. For other parameters, the starting guesses were inspired by corresponding values in our 192 OsO 4 study [22][23][24], but vary more substantially. Below 320 cm -1 the most prominent feature is the ν 2 Q-branch, constituted by relatively evenly spaced line clusters split by centrifugal effects.…”

“…Such a Hamiltonian development scheme enables the treatment of any polyad system. The ν 2 and the ν 4 harmonic wavenumbers being close to each other, as mentioned above, we a priori consider that the two stretching fundamentals form a ν 2 / ν 4 dyad, just as for the OsO 4 case [24]. Thus, we build up the following effective Hamiltonians:…”

“…High resolution (0.001 cm -1 ) spectra of the ν 2 /ν 4 region of pure 102 RuO 4 have been recorded. Using the tensorial formalism and methods developed previously [18][19][20][21], spectra are analyzed in detail and compared to its heavier analogue, osmium tetroxide [22][23][24]. Assignments are performed up to high J rotational quantum number values.…”

Infrared spectroscopy of ruthenium tetroxide and high-resolution analysis of the ν3 band

“…More exactly, the determination of the electronic and geometrical structure of molecules containing heavy transition metal elements (like ruthenium or osmium) is a severe test of the ab initio methods and, in particular, of their ability to take into account relativistic effects for the core electrons of heavy metal compounds. Contrary to OsO 4 [14][15][16][17], RuO 4 has been less studied until now.…”