Chirped-pulse Fourier Transform Microwave Spectrometer Research Articles

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave spectroscopy

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is presented. A new CP-FTMW spectrometer capable of measuring the entire 7.5–18.5 GHz spectrum with a single polarizing pulse is described briefly. The CP-FTMW spectrometer takes advantage of recent advances in digital electronics by utilizing a 4.2 GS/s arbitrary waveform generator as a frequency source and a 12 GHz digital oscilloscope to digitize the down converted molecular free induction decay (FID). Signal averaging in the time domain is used to increase the signal-to-noise ratio. The rotational constants of three unique conformers of epifluorohydrin were measured, as well as the rotational constants of the three unique 13C isotopomers and the 18O isotopomer (in natural abundance) of the most stable conformer. The rotational constants of the two less stable conformers differ significantly from those previously reported [F.G. Fujiwara, J.L. Painter, H. Kim, J. Mol. Struct. 41 (1977) 169–175]. Ab initio calculations were performed for all three conformations and are compared to experimental values.

OECD report outlines water management improvements

Microwave spectra of 9-fluorenone and benzophenone have been observed using a broadband chirped-pulse Fourier Transform Microwave (cp-FTMW) Spectrometer. An analysis of the microwave spectra allowed for the assignment of 178 b-type rotational transitions for 9-fluorenone in the 8.0–13.0 GHz region, the assignment of 166 b-type transitions for benzophenone in the 8.0–14.0 GHz region, and effectively quadrupled the total number of pure rotational transitions observed for these molecules. This new microwave data and the previously published millimeter wave data of Maris et al. have been analyzed together in a global fit, where the resulting rotational constants accurately reproduce the spectra over the entire 8–80 GHz region for both molecules. In addition, the resulting constants have been found to be consistent with the expected planar C2v structure for 9-fluorenone and the paddle-wheel like C2 structure of benzophenone. The rotational constants of the combined global fit have allowed for a more precise determination of the inertial defects (Δ) and second moments of inertia (Pcc) for 9-fluoreneone and benzophenone. Specific focus has been paid to the second moment of benzophenone, which when used in conjunction with theory strongly suggests an ∼32.9° torsional angle out of the ab-plane for the paddle-wheel structure of the gas-phase molecule.