The spectroscopic analysis of the v2=1, v5=1, and v3=v6=1 infrared vibration system of H3SiI.

The ν2 (A1)/ν5 (E)/ν3+ν6 (E) band system of H3(28)SiI was investigated using Fourier transform infrared spectra recorded from 820 to 1100 cm(-1) at a resolution of 2.0×10(-3) cm(-1). In total, 11,903 transitions were assigned. Additional 1466 transitions reaching the v3=v6=1 state were obtained from the ν3+ν6-ν6 and ν3+ν6-ν3 hot bands near 360 and 590 cm(-1), respectively. Moreover, 30 highly accurate CO2 laser sideband transitions of the (r)Q0 branch of ν5 (J.M. Frye, W. Schupita, and G. Magerl, J. Mol. Spectrosc. 128, 427 (1988)) were implemented in the data set with J(max)″=140 and K(max)″=21. To adequately reproduce the complex pattern of interacting levels the Hamiltonian employed included 14 off-diagonal terms. These comprise x,y Coriolis ro-vibration resonances, between ν2/ν5, ν2/ν3+ν6 and ν5/ν3+ν6, and the anharmonic Fermi resonance between ν5/ν3+ν6. All these resonances strongly perturb the v2=1, v5=1, and v3=v6=1 excited states whose rounded deperturbed vibrational term values are 904.5, 941.1, and 953.7 cm(-1), respectively. In addition, the Δl=Δk=±2 l-resonance was found to be active within the v3=v6=1 state and between v5=1 and v3=v6=1; the Δl=±2,Δk=∓1 l-resonance within the v5=1 state and between v5=1 and v3=v6=1 was established, as well as the Δl=±1,Δk=∓2 α resonance between v2=1 and v5=1. A standard deviation of the fit, 0.48×10(-3) cm(-1), resulted which is ca. three times the estimated precision of experimental wavenumbers. Improved J-dependent ground state parameters of H3SiI were obtained by fitting 5420 combination differences, σ(fit)=0.22×10(-3) cm(-1).

The experimental equilibrium structure of acetylene.

The empirical equilibrium structure of acetylene has been derived by exploiting the very precise experimental rotational constants available in the literature for the 10 isotopologues relative to all the possible combinations of H, D, (12)C and (13)C atoms. The geometry obtained when data for all species are fitted together is: re(CH) = 106.167(14) pm and re(CC) = 120.2866(72) pm. This determination shows some systematic residuals due to the singly D-substituted isotopologues. If we exclude such species from the fit, we obtain our most precise evaluation: re(CH) = 106.1689(23) pm and re(CC) = 120.2817(12) pm. The possibility of a breakdown of the Born-Oppenheimer approximation has also been tested.

The infrared spectrum of (12)C2D2: the stretching-bending band system up to 5500 cm(-1).

The infrared spectrum of the perdeuterated acetylene, (12)C2D2, has been recorded from 900 cm(-1) to 5500 cm(-1) by Fourier transform spectroscopy at a resolution ranging between 0.004 and 0.009 cm(-1). Ninety-two bands involving the ν1, ν2, and ν3 stretching modes, also associated with the ν4 and ν5 bending vibrations and 9 bands involving pure bending transitions have been observed and analysed. In total, 8345 transitions for the stretching-bending, and 862 for the pure bending modes have been assigned in the investigated spectral region. All the transitions relative to each stretching mode, i.e. the fundamental, its first overtone, and associated hot and combination bands involving bending states up to v4 + v5 = 2, were fitted simultaneously. The Hamiltonian adopted for the analysis is that appropriate to a linear molecule and includes vibration and rotation l-type interactions. The Darling-Dennison interaction between v4 = 2 and v5 = 2 levels associated with the various stretching states was also considered. The standard deviation for each global fit is smaller than 0.0006 cm(-1), of the same order of magnitude of the measurement precision.

Ab initio quartic force field of stannane and rotational analysis of the ν1 infrared band of H(120)SnD3.

Stannane, SnH(4), has been studied both theoretically, using high-level ab initio methods, and experimentally, using high-resolution spectroscopy to analyze the Sn-H stretching fundamental band of the H(120)SnD(3) isotopologue. The geometry and the anharmonic force field of the molecule have been calculated ab initio, using the coupled-cluster with single, double, and perturbative triple excitations level of theory. H(120)SnD(3), present as minor isotopologue in (120)SnD(4), has been studied by Fourier transform spectroscopy at an effective resolution of ca. 0.005 cm(-1) near 1900 cm(-1) and the ν(1) band was identified. About 360 ro-vibration transitions with J(') up to 18 and K up to 10 have been assigned. Since the spectrum evidenced the existence of some perturbations, the transitions were analyzed either neglecting, or including in the model A(1)∕E Coriolis-type interactions with nearby dark states. The standard deviation of the fits, ca. 1.5 × 10(-3) cm(-1), is about one order of magnitude larger than the estimated experimental precision, and is only slightly dependent on the adopted model. The spectroscopic parameters obtained from this and from previous analyses of stannane isotopologues have been compared with the theoretical results. The theoretical force field is also used to obtain semi-experimental harmonic frequencies and the equilibrium geometry.

Ab initio anharmonic force field and rotational analyses of infrared bands of perchloryl fluoride.

Perchloryl fluoride, FClO(3), has been studied both experimentally and theoretically, using high-resolution Fourier transform spectroscopy and high-level ab initio methods. The geometry, dipole moment, and anharmonic force field of the molecule have been calculated ab initio, using the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] level of theory. The infrared spectra of monoisotopic species have been recorded. The nu(1) + nu(2) bands of F(35)Cl(16)O(3), F(37)Cl(16)O(3), F(35)Cl(18)O(3), and F(37)Cl(18)O(3), the nu(2) + nu(3) and nu(2) + nu(3) - nu(3) bands of F(35)Cl(16)O(3) and F(37)Cl(16)O(3), and the 2nu(3) - nu(3) band of F(37)Cl(16)O(3) have been analyzed. The spectroscopic parameters obtained from these and from previous analyses have been compared with the theoretical results.