The structural and conformational properties of 1-fluorocyclopropanecarboxylic acid have been explored by microwave spectroscopy and a series of ab initio (MP2/6-311++G(d,p) level), density functional theory (B3LYP/aug-cc-pVTZ level), and G3 quantum chemical calculations. Four “stable” conformers, denoted conformers I−IV, were found in the quantum chemical calculations, three of which (conformers I −III) were predicted to be low-energy forms. Conformer I was in all the quantum chemical calculations predicted to have the lowest energy, conformer III to have the second lowest energy, and conformer II to have the third lowest energy. Conformers II and III were calculated to have relatively large dipole moments, while conformer I was predicted to have a small dipole moment. The microwave spectrum was investigated in the 18−62 GHz spectral range. The microwave spectra of conformers II and III were assigned. Conformer I was not assigned presumably because its dipole moment is comparatively small. Conformer II i...

A Microwave and Quantum Chemical Study of the Conformational Properties and Intramolecular Hydrogen Bonding of 1-Fluorocyclopropanecarboxylic Acid

The rotational transitions of CO in the electronically excited states (a 3Πr and a’ 3Σ+) are observed in the millimeter and submillimeter wave regions. The vibrational satellites are detected up to v=6 for the a 3Πr state and up to v=2 for the a’ 3Σ+ state. The observed spectra are found to be perturbed by the interaction between the a 3Πr and a’ 3Σ+ states, and they are not fitted to conventional formulations for the 3Πr and 3Σ+ states within the experimental uncertainties. A simultaneous deperturbation analysis for the a 3Πr (v=0–7) states and the a’ 3Σ+(v=0–3) states is carried out by using the observed transition frequencies and the reported data of the Λ‐type doubling rf transitions in the a 3Πr state. The detailed molecular constants are obtained for the a 3Πr and a’ 3Σ+ states. These constants show smooth change on the vibrational quantum number. This indicates that they are almost free from the interaction between the a 3Πr and a’ 3Σ+ states.

The microwave spectra of CO in the electronically excited states (a 3Πr and a’ 3Σ+)

The 220 ← 221 transition of H2D+ was detected by using a dc discharge in a mixture of H2 and D2 with a hollow cathode cooled to liquid nitrogen temperature. The assignment was made on the basis of chemistry for production, the observed linewidth, and the lowering of the spectral intensity by the external magnetic field. The transition frequency was determined to be 155 987.185±0.037 MHz.

The microwave spectrum of the H2D+ ion: The 220 ← 221 transition

Rotational spectroscopy is introduced as a new in situ method for monitoring gas-phase reactants and products during chemical reactions. Exploiting its unambiguous molecular recognition specificity and extraordinary detection sensitivity, rotational spectroscopy at terahertz frequencies was used to monitor the decomposition of carbonyl sulfide (OCS) over an aluminum nanocrystal (AlNC) plasmonic photocatalyst. The intrinsic surface oxide on AlNCs is discovered to have a large number of strongly basic sites that are effective for mediating OCS decomposition. Spectroscopic monitoring revealed two different photothermal decomposition pathways for OCS, depending on the absence or presence of H2O. The strength of rotational spectroscopy is witnessed through its ability to detect and distinguish isotopologues of the same mass from an unlabeled OCS precursor at concentrations of <1 nanomolar or partial pressures of <10 μTorr. These attributes recommend rotational spectroscopy as a compelling alternative for monit...

Monitoring Chemical Reactions with Terahertz Rotational Spectroscopy

Microwave spectroscopy of MgO in the a3Π and X1Σ states

Peak absorption coefficients αmax for the J = 1←O,J = 2←1 and J = 3←2 rotational transitions in carbonyl sulphide have been calculated for the different isotopic molecular species in natural abundance and in each case for a range of vibrational states. The results are tabulated for convenience both in order of values of αmax and in order of transition frequencies. Calculations have also been made, on a less extensive basis, for transitions from J = 4←3 to J = 25←24, and peak absorption coefficients have been tabulated, in order of values of αmax, for each of these transitions. The tables provide a frequency coverage of approximately 10 to 300 GHz. Comparison with available experimental results shows satisfactory agreement.

Z. Kisiel

Papers

Peak Absorption Coefficients of Microwave Absorption Lines of Carbonyl Sulphide