ABSTRACT
Dialuminum monoxide, Al2O, has been investigated in the laboratory at mid-IR wavelengths around 10 µm at high spectral resolution. The molecule was produced by laser ablation of an aluminum target with the addition of gaseous nitrous oxide, N2O. Subsequent adiabatic cooling of the gas in a supersonic beam expansion led to rotationally cold spectra. In total, 848 ro-vibrational transitions have been assigned to the fundamental asymmetric stretching mode ν3 and to five of its hot bands, originating from excited levels of the ν1 symmetric stretching mode and the ν2 bending mode. The measurements encompass 11 vibrational energy states (v1 v2l v3). The ro-vibrational transitions show spin statistical line intensity alternation of 7:5, which is caused by two identical aluminum nuclei of spin I = 5/2 at both ends of the centrosymmetric molecule of structure Al-O-Al. The less effective cooling of vibrational states in the supersonic beam expansion allowed measurement of transitions in excited vibrational states at energies of 1000 cm-1 and higher, while rotational levels within vibrational modes exhibited thermal population, with rotational temperatures around Trot = 115 K. Molecular parameters for 11 vibrational states were derived, including rotation and centrifugal distortion constants and l-type doubling constants for the states (v1 v2l v3) = (0 11 0) and (0 11 1) and an l-type resonance between the states (0 20 0) - (0 22 0) and (0 20 1) - (0 22 1). From the experimental results, rotational correction terms and the equilibrium bond length re were derived. The measurements were supported and guided by high-level quantum-chemical calculations that agree well with the derived experimental results.
ABSTRACT
The ν3 antisymmetric stretching mode of disilicon-carbide, Si2C, was studied using a narrow line width infrared quantum cascade laser spectrometer operating at 8.3 µm. The Si2C molecules were produced in an Nd:YAG laser ablation source from a pure silicon sample with the addition of a few percent methane diluted in a helium buffer gas. Subsequent adiabatic expansion was used to cool the gas down to rotational temperatures of a few tens of kelvin. A total of 183 infrared transitions recorded in the spectral range between 1200 and 1220 cm-1 were assigned to the fundamental ν3 mode of Si2C. In addition, pure rotational transitions of Ka = 1 and 2 between 278 and 375 GHz were recorded using a supersonic jet spectrometer for submillimeter wavelengths. Molecular parameters for the ( v1 v2 v3) = (001) vibrationally excited state were derived and improved molecular parameters for the vibrational ground-state (000) were obtained from a global fit data analysis, which includes our new laboratory data and millimeter wavelength data from the literature. We found the rotational levels Ka = 0 and Ka = 2 in the vibrationally excited (001) state being perturbed by a Coriolis-type interaction with energetically close lying levels of the symmetric stretching and triple-excited bending mode (130). The data analysis was supported by quantum chemical calculations performed at the coupled-cluster level of theory. All experimental results were found to be in excellent agreement with the theory.
