The prediction of far-infrared spectra for planetary nitrile ices using periodic density functional theory with comparison to thin film experiments.

Future spacecraft missions to planetary systems, Trans-Neptunian objects, and cometary bodies could implement far-infrared surveys to confirm the presence of condensed-phase species via their unique lattice features. For composite molecular ices of astrophysical significance, laboratory reference spectra are required to provide absorption coefficients used to quantify solid-state abundances. However, due to strong intermolecular interactions in polar ice systems, laboratory data of mixed-phase ices are difficult to interpret. In this study we have applied periodic density functional theory code to model bulk molecular crystals. This method allows for more accurate simulation of thin-film spectra than approaches simulating small clusters. For this proof-of-principle study on a series of pure nitrile ices of planetary interest, our simulated far-infrared spectra show excellent agreement to data from thin film studies performed at the Australian Synchrotron (crystalline acetonitrile and propionitrile) and to previously published spectra (hydrogen cyanide, acrylonitrile, cyanoacetylene, and cyanogen). The combined theoretical and experimental approach has provided a new explanation for the asymmetric profile of the hydrogen cyanide lattice feature and a more systematic assignment of nitrile ice absorption bands to low-frequency lattice modes. We nominate prominent absorption features for the detection of crystalline nitrile carriers located on planetary surfaces.

Methods and methodology for FTIR spectral correction of channel spectra and uncertainty, applied to ferrocene.

We present methodology for the first FTIR measurements of ferrocene using dilute wax solutions for dispersion and to preserve non-crystallinity; a new method for removal of channel spectra interference for high quality data; and a consistent approach for the robust estimation of a defined uncertainty for advanced structural χr2 analysis and mathematical hypothesis testing. While some of these issues have been investigated previously, the combination of novel approaches gives markedly improved results. Methods for addressing these in the presence of a modest signal and how to quantify the quality of the data irrespective of preprocessing for subsequent hypothesis testing are applied to the FTIR spectra of Ferrocene (Fc) and deuterated ferrocene (dFc, Fc-d10) collected at the THz/Far-IR beam-line of the Australian Synchrotron at operating temperatures of 7K through 353K.

Structural, vibrational, and rovibrational analysis of tetrafluoroethylene.

High resolution FTIR spectra of (13)C enriched tetrafluoroethylene (C(2)F(4)) were measured at 150 K at the Australian Synchrotron. Rovibrational transitions were assigned in the a-type symmetric and b-type antisymmetric CF(2) stretches of (12)C(13)CF(4) and (13)C(2)F(4) near 1170 cm(-1) and 1300 cm(-1), respectively. Ground vibrational state spectroscopic constants for both molecules were determined in addition to the upper state constants for ν(11) and ν(9) of (13)C(2)F(4) and ν(11), ν(2)+ν(6), and ν(5) of (12)C(13)CF(4). The ground state constants, along with those determined for the (12)C(2)F(4) isotopologue from previously published data, were used to determine a semi-experimental r(e) structure r(CC) = 132.36 ± 0.37 pm, r(CF) = 131.11 ± 0.23 pm, α(FCC) = 123.3 ± 0.3° in excellent agreement with ab initio structures. Lower resolution FTIR spectra were measured between 100 and 5000 cm(-1) at room temperature and band centres obtained for all modes of the three isotopologues; although only 5 out of 12 modes in (12)C(2)F(4) and (13)C(2)F(4) are infrared (IR) active, the others were inferred from combination and hot-band positions. A number of modes are observed to be infrared active only in the (12)C(13)CF(4) isotopologue due to its lower symmetry. Most notably, decoupling of the antisymmetric CF(2) motions in the two halves of (12)C(13)CF(4) results in 2 strongly IR active modes that involve motion at one carbon or the other.

Fourier transform infrared emission spectra of MgH and MgD.

High resolution Fourier transform infrared emission spectra of MgH and MgD have been recorded. The molecules were generated in an emission source that combines an electrical discharge with a high temperature furnace. Several vibration-rotation bands were observed for all six isotopomers in the X (2)Sigma(+) ground electronic state: v=1-->0 to 4-->3 for (24)MgH, v=1-->0 to 3-->2 for (25)MgH and (26)MgH, v=1-->0 to 5-->4 for (24)MgD, v=1-->0 to 4-->3 for (25)MgD and (26)MgD. The new data were combined with the previous ground state data, obtained from diode laser vibration-rotation measurements and pure rotation spectra, and spectroscopic constants were determined for the v=0 to 4 levels of (24)MgH and the v=0 to 5 levels of (24)MgD. In addition, Dunham constants and Born-Oppenheimer breakdown correction parameters were obtained in a combined fit of the six isotopomers. The equilibrium vibrational constants (omega(e)) for (24)MgH and (24)MgD were found to be 1492.776(7) cm(-1) and 1077.298(5) cm(-1), respectively, while the equilibrium rotational constants (B(e)) are 5.825 523(8) cm(-1) and 3.034 344(4) cm(-1). The associated equilibrium bond distances (r(e)) were determined to be 1.729 721(1) A for (24)MgH and 1.729 157(1) A for (24)MgD.