In this study, we present the ro-vibrationally resolved gas-phase spectrum of the diatomic molecule TiO around 1000 cm −1 . Molecules were produced in a laser ablation source by vaporizing a pure titanium sample in the atmosphere of gaseous nitrous oxide. Adiabatically expanded gas, containing TiO, formed a supersonic jet and was probed perpendicularly to its propagation by infrared radiation from quantum cascade lasers. Fundamental bands of 46−50 TiO and vibrational hotbands of 48 TiO are identified and analyzed. In a mass-independent fitting procedure combining the new infrared data with pure rotational and electronic transitions from the literature, a Dunham-like parameterization is obtained. From the present data set, the multi-isotopic analysis allows to determine the spin-rotation coupling constant γ and the Born-Oppenheimer correction coefficient ∆ Ti U 10 for the first time. The parameter set enables to calculate the Born-Oppenheimer correction coefficients ∆ Ti U 02 and ∆ O U 02 . In addition, the vibrational transition moments for the observed vibrational transitions are reported.
Propylene oxide, CH 3 C 2 H 3 O, is a stable chiral molecule that gained new attention through its recent radio astronomical discovery in the interstellar medium toward the galactic center a . Subsequently, extensive laboratory data on rotational transitions in the ground state and in the lowest vibrationally excited ν 24 torsion state were published b,c . Previously, only the 3 µm spectral range of the four C-H stretching vibration modes was measured with high spectral resolution at mid-infrared wavelength d .In the present study we used two quantum cascade laser spectrometers at 8 and 10 µm to record ro-vibrational spectra of the ν 17 fundamental mode (CH 2 rock) at 1023 cm −1 and the ν 12 ring breathing mode at 1266 cm −1 . The spectra were measured in a static cell at room temperature and in a supersonic jet expansion at low temperatures. The room temperature measurement allowed a quick assignment via graphical techniques (Loomis-Wood diagram) and determination of the molecular parameters using the SPFIT/SPCAT program package e . In the supersonic jet spectrum line splittings could be observed for certain transitions. The combination of measurements at low temperature (30K) and at room temperature conditions led to an assignment of hundreds of transitions of the very dense infrared spectrum and covers quantum numbers from lowest J and K up to J = 55 and K a = 36.
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 (v 1 v 2 l v 3). 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 T rot = 115 K. Molecular parameters for 11 vibrational states were derived, including rotation and centrifugal distortion constants and l-type doubling constants for the states (v 1 v 2 l v 3) = (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 r e were derived. The measurements were supported and guided by high-level quantum-chemical calculations that agree well with the derived experimental results.
Small molecules made of refractory materials are thought to play an important role in the dust formation processes around late-type stars. Likewise, they take part in the opacity process of variable late-type stars, as has been shown for the molecule TiO. a Because of similar formation conditions, the diatomic molecule vanadium oxide (VO) is thought to occur in similar locations around stars as TiO. b VO has already been detected in the near-infrared region in the envelope of the red hypergiant VY CMa c , but due to the lack of high-resolution laboratory spectra, no astrophysical search of VO in the mid-IR region has been performed. In this work, we report the ro-vibrational absorption spectrum of X 4 Σ − VO, including its hyperfine structure. In our experiment we used a frequency modulated quantum cascade laser in combination with Herriott-type multipass optics. The molecules were produced by laser ablation of a vanadium rod and an N 2 O/He buffer gas, which was subsequently adiabatically expanded into a vacuum chamber. The rotationally cooled spectrum was analyzed using the pgopher software and the molecular constants were determined. The experimental data as well as line predictions will enable a dedicated search for this molecule in space at mid-IR wavelengths.
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