LOCAL-MODE EFFECTS ON THE ROTATIONAL STRUCTURE OF THE 1ST STRETCHING OVERTONE BAND SYSTEM OF STIBINE, SBH3

A high-resolution Fourier-transform infrared spectrum, resolution about 0.006 cm-1, of the first stretching overtone band system of stibine has been measured and rotationally analyzed in detail up to J' = 22 for both (SbH3)-Sb-121 and (SbH3)-Sb-123 isotopic species. The rotational levels of the A1 and E vibrational states have been analyzed simultaneously by including vibration-rotation coupling terms in the Hamiltonian for the two isotopic species. The A1/E vibrational energy-level separation has been found to be 0.0727 (8) cm-1 for (SbH3)-Sb-121 and 0.0763 (8) cm-1 for (SbH3)-Sb-123 with the A1 state being higher in energy in both cases. Fits including 1445 transitions with the standard deviation of 0.0024 cm-1 for (SbH3)-Sb-121 and 1322 transitions with the standard deviation of 0.0022 cm-1 for (SbH3)-Sb-123 have been obtained by optimizing altogether 33 upper-state parameters in both cases. A simple local-mode model is shown to account very well for the vibrational dependence of the rotational constants and the coefficients of vibrationally off-diagonal H22 operators.