Structure of the Alkali Hydroxides. IV. Interpretation of Vibration–Rotation Interactions in CsOH and RbOH and Refinement of Structures

Abstract

A new formulation of the vibration–rotation interactions in linear triatomic molecules is developed for the purpose of explaining the anomalies found in the microwave spectra of CsOH and RbOH. This formulation, which explicitly takes into account the curvilinear nature of the motions, leads to a some-what different partitioning of the interaction constant α2 into harmonic and anharmonic contributions. The harmonic contribution resulting from direct averaging of the moment of inertia over the bending mode is found to dominate the α2 constant in most linear molecules, in contrast to the traditional treatment, which leads to a large anharmonic contribution. In the alkali hydroxides the harmonic and anharmonic parts are comparable in magnitude but of opposite sign; the resulting cancellation is responsible for the unusual vibrational dependence of Bυ in these molecules. The deuterium isotope shifts of Bυ are in excellent agreement with the predictions of this treatment. All of the microwave and infrared data on CsOH and RbOH are consistent with a reasonable force field, although uncertainties in the harmonic force constants prevent a quantitative determination of anharmonic constants. In the absence of contrary evidence, we conclude that the alkali hydroxides very probably have a linear equilibrium configuration. The equilibrium bond lengths in CsOH are estimated to be: rCsO. = 2.391 Å, rOH = 0.960 Å; in RbOH: rRbO = 2.301 Å, rOH = 0.957 Å.

The CaCCHÃ2Π–2Σ+522and 520Bands Studied by High Resolution Spectroscopy: The Ca–C–C Bending Vibration and Vibronic Interaction

“…(6) that B £ is dependent on both quantum numbers £ and l in a bands. bending mode (15). We also noticed that mixing between As seen from ; the B value is slightly larger, the vibronic energy, were found quite different from those and the D value is much larger than the corresponding values predicted by the global fit.…”

“…It can also be verified that the spin-orbit operator does not 2 /4.4 Å 2.384 [13] for the [15] for the £ 5 Å 3 2 G 7/2 Ç £ 5 Å 2 2 F 7/2 interaction. Here, the denominators are the unperturbed energy separations (cm 01 ) of the two mutually perturbing levels.…”

“…We thus obtain the absolute value for the parameter F as 3.24, 3.17, and 2.76 cm 01 , respectively, from Eqs. [13], [14], and [15], and the average is ÉFÉ Å 3.06 cm 01 . We may now evaluate more quantities using Eq.…”

The ν3and ν3+ ν5Vibration Levels in the CaCCHX̃2Σ+State

“…The Ca -C -C bending mode, on the other hand, the correstandard deviation of the fit was s P Å 0.01 cm 01 which is sponding constant was found negative, a 5 É 00.00121 in accord with the experimental precision. Since the low cm 01 , indicating a dominant contribution from the harresolution ( 0.1 cm 01 ) of the DF spectra did not resolve monic force field in the curvilinear coordinate potential the small spin -rotation splittings, the spin -rotation con- ( 11 ) . When the n 3 and n 5 modes were simultaneously stant for the lower state could not be fitted and was fixed excited by one quantum from the ground vibration level, at the value for the ground vibration level; this should be the change of B £ was found essentially equal to the algea good approximation.…”

Vibration-Rotation Interaction in the Microwave Spectrum of KOH

“…Rotation vibration interaction is of particular interest for these molecules because of the extremely large amplitude of the bending motion 7 ' 8 . For CsOH it has been shown that the dependence of the rotational constant on the quantum numbers v2 and I can be fitted to the usual expression In the present investigation more than 50 lines of the rotational transition / = 6^-5 have been measured for the two isotopic species 39 KOH and 41 KOH with an experimental error of only a few parts in 10 6 .…”