The microwave spectrum of sodium tetrahydroborate NaBH4 in excited vibrational states: Coriolis interaction between the Na-BH4 stretching and the BH4 rocking vibrations

Abstract

Two sets of vibrational satellites have been observed in the rotational spectrum of sodium tetrahydroborate NaBH4, and have been assigned to the non-degenerate, Na—BH4 stretching and the degenerate BH4 rocking (or internal rotation) states. The observation was extended from the J = 11 ← 10 up to J = 20 ← 19 transitions. The vibrational satellites showed anomalous K structure; higher-K lines of the non-degenerate state appeared at higher frequencies, in reverse to those of the ground state, whereas the spectra in the degenerate state exhibited a K pattern similar to but somewhat more widely spread than that of the ground state. These anomalies are ascribed to the Coriolis interaction between the two excited vibrational states. The spectra observed were analysed using a C3v symmetric-top rotational Hamiltonian, which took into account the Coriolis interaction explicitly. The A rotational constants, the energy difference δE between the two interacting vibrational states, and the first- and second-order Coriolis interaction constants have been derived.