Microwave spectrum of the inversion-rotation transitions of the D3O+ ion:: Δk = ±3n interaction and equilibrium structure

Ground state inversion-rotation transitions of the fully deuterated hydronium ion, D3O+, were observed by microwave spectroscopy. Fifty three P- and Q-branch transitions were measured precisely for the lowest pair of inversion doublets in the frequency region of 220 to 565 GHz. Inclusion of Delta k = +/-3n interactions in the Hamiltonian was essential for a full explanation of the observed lines, with measurement uncertainty of 20 to 60 kHz. The molecular constants, including C, for the 0(+) and 0(-) levels, as well as the Delta k = +/-3n interaction parameters, were determined from this complete fitting to the data. The inversion splitting was determined to be 15.355 503 38(107) cm(-1), where the number in parentheses denotes one standard deviation of the fit. Since a harmonic potential of H3O+ is available, zero-point corrections to the rotational constants of H3O+ and D3O+ were calculated and the zero-point averaged (r(z)) structures were derived from the zero-point corrected rotational constants. The results are as follows: D3O+(0(+)) : r(z) = 0.981 8(23)Angstrom, theta(z) = 112.68(100)degrees, D3O+(0(-)) : r(z) = 0.983 0(23)Angstrom, theta(z) = 112.02(100)degrees. From the shift between the I, structures of H3O+ and D3O+ the r(e) structure of H3O+ was estimated to be r(e) = 0.970 2(89)Angstrom, theta(e) = 109.4(38)degrees.