Millimeter-wave rotational spectroscopy of FeCN (X 4Δi) and FeNC (X 6Δi): Determining the lowest energy isomer

Prebiotic Astrochemistry from Astronomical Observations and Laboratory Spectroscopy

The discovery of more than 200 gas-phase chemical compounds in interstellar space has led to the speculation that this nonterrestrial synthesis may play a role in the origin of life. These identifications were possible because of laboratory spectroscopy, which provides the molecular fingerprints for astronomical observations. Interstellar chemistry produces a wide range of small, organic molecules in dense clouds, such as NH2COCH3, CH3OCH3, CH3COOCH3, and CH2(OH)CHO. Carbon (C) is also carried in the fullerenes C60 and C70, which can preserve C-C bonds from circumstellar environments for future synthesis. Elusive phosphorus has now been found in molecular clouds, the sites of star formation, in the molecules PO and PN. Such clouds can collapse into solar systems, although the chemical/physical processing of the emerging planetary disk is uncertain. The presence of molecule-rich interstellar starting material, as well as the link to planetary bodies such as meteorites and comets, suggests that astrochemical processes set a prebiotic foundation.

The structure of ScC2 (X̃2A1): A combined Fourier transform microwave/millimeter-wave spectroscopic and computational study

Pure rotational spectra of Sc¹³C₂ (X̃²A₁) and Sc¹²C¹³C (X̃²A') have been measured using Fourier transform microwave/millimeter-wave methods. These molecules were synthesized in a DC discharge from the reaction of scandium vapor, produced via laser ablation, with ¹³CH₄ or ¹³CH₄/¹²CH₄, diluted in argon. The N_Ka,Kc = 1_0,1 → 0_0,0, 2_0,2 → 1_0,1, 3_0,3 → 2_0,2, and 4_0,4 → 3_0,3 transitions in the frequency range of 14 GHz-61 GHz were observed for both species, each exhibiting hyperfine splittings due to the nuclear spins of ¹³C (I = 1/2) and/or Sc (I = 7/2). These data have been analyzed with an asymmetric top Hamiltonian, and rotational, spin-rotation, and hyperfine parameters have been determined for Sc¹³C₂ and Sc¹²C¹³C. In addition, a quartic force field was calculated for ScC₂ and its isotopologues using a highly accurate coupled cluster-based composite method, incorporating complete basis set extrapolation, scalar relativistic corrections, outer core and inner core electron correlation, and higher-order valence correlation effects. The agreement between experimental and computed rotational constants, including the effective constant (B + C), is ∼0.5% for all three isotopologues. This remarkable agreement suggests promise in predicting rotational spectra of new transition metal-carbon bearing molecules. In combination with previous work on Sc¹²C₂, an accurate structure for ScC₂ has been established using combined experimental (B, C) and theoretical (A) rotational constants. The radical is cyclic (or T-shaped) with r_(Sc-C) = 2.048(2) Å, r_(C-C) = 1.272(2) Å, and ∠_(C-Sc-C) = 36.2(1)°. The experimental and theoretical results also suggest that ScC₂ contains a C₂ ^- moiety and is largely ionic.

Alkaline and Alkaline-earth Cyanoacetylides: A Combined Theoretical and Rotational Spectroscopic Investigation

The metallic cyanoacetylides LiC3N, NaC3N, MgC3N and CaC3N have been investigated by combined spectroscopy measurements and theoretical calculations. The theoretical calculations predict for the four species that the linear isomer with formula MCCCN (M= Li, Na, Mg and Ca) is the most stable one. We used the laser ablation molecular beam Fourier transform microwave spectroscopy to synthesize these species by the reaction of metal vapors, produced by laser ablation, and the 3-bromo-2-propynenitrile (BrCCCN). The pure rotational spectra were observed by Fourier transform microwave spectroscopy in the 2-18 GHz frequency region only for LiCCCN and NaCCCN, while no spectral signatures for MgCCCN and CaCCCN could be detected. Finally, we have searched for LiCCCN and NaCCCN species towards the carbon-rich evolved star IRC + 10216 but only upper limits to their abundances have been obtained.

Discovery of the first Ca-bearing molecule in space: CaNC

We report on the detection of calcium isocyanide, CaNC, in the carbon-rich evolved star IRC+10216. We derived a column density for this species of (2±0.5)×1011 cm-2. Based on the observed line profiles and the modelling of its emission through the envelope, the molecule has to be produced in the intermediate and outer layers of the circumstellar envelope where other metal-isocyanides have previously been found in this source. The abundance ratio of CaNC relative to MgNC and FeCN is ≃1/60 and ≃1, respectively. We searched for the species CaF, CaCl, CaC, CaCCH, and CaCH3 for which accurate frequency predictions are available. Only upper limits have been obtained for these molecules.

Towards a quantum chemical protocol for the prediction of rovibrational spectroscopic data for transition metal molecules: Exploration of CuCN, CuOH, and CuCCH

High accuracy electronic structure computations for small transition metal-containing molecules have been a long term challenge. Due to coupling between electronic and nuclear wave functions, even experimental/theoretical identification of the ground electronic state requires tremendous efforts. Quartic force fields (QFFs) are effective ab initio tools for obtaining reliable anharmonic spectroscopic properties. However, the method that employs complete basis set limit extrapolation ("C"), consideration of core electron correlation ("cC"), and inclusion of scalar relativity ("R") to produce the energy points on the QFF, the composite CcCR methodology, has not yet been utilized to study inorganic spectroscopy. This work takes the CcCR methodology and adapts it to test whether such an approach is conducive for the closed-shell, copper-containing molecules CuCN, CuOH, and CuCCH. Gas phase rovibrational data are provided for all three species in their ground electronic states. Equilibrium geometries and many higher-order rovibrational properties show good agreement with earlier studies. However, there are notable differences, especially in computation of fundamental vibrational frequencies. Even with further additive corrections for the inner core electron correlation and coupled cluster with full single, double, and triple substitutions (CCSDT), the differences are still larger than expected indicating that more work should follow for predicting rovibrational properties of transition metal molecules.

Metallic cyanoacetylides of copper, silver and gold: generation and structural characterization

Copper, silver and gold cyanoacetylides have been synthesized and characterized in the laboratory using a combination of a laser ablation technique and Fourier transform microwave spectroscopy. A study of the chemical bonding helps to understand the preference for metal–C bonding over metal–N bonding.