Denis Petitprez

Chlorofluoroiodomethane as a potential candidate for parity violation measurements

CHFClI is among the more favorable molecules for parity violation (PV) measurements in molecules. Despite the fact that calculated PV effects are two orders of magnitude smaller than in some organometallic compounds, CHFClI displays interesting features which could make possible a new experimental PV test on this molecule. Indeed, ultrahigh resolution spectroscopy using an ultrastable CO(2) laser is favored by several intrinsic properties of this molecule. For example, the high vapor pressure of CHFClI allows investigation by supersonic beam spectroscopy. Indeed, the spectroscopic constants have been accurately determined by microwave and millimetre wave spectroscopy. This is important for the subsequent selection of an appropriate absorption band of CHFClI that could be brought to coïncide with the absorption of CO(2). Partially resolved (+)- and (-)-CHFClI enantiomers with respectively 63.3 and 20.5% ees have been recently prepared and analyzed by molecular recognition using chiral hosts called cryptophanes. Finally, the S-(+)/R-(-) absolute configuration was ascertained by vibrational circular dichroïsm (VCD) in the gas phase.

Sensitive and selective detection of OH radicals using Faraday rotation spectroscopy at 2.8 µm.

We report on the development of a Faraday rotation spectroscopy (FRS) instrument using a DFB diode laser operating at 2.8 µm for the hydroxyl (OH) free radical detection. The highest absorption line intensity and the largest gJ value make the Q (1.5) double lines of the 2Π3/2 state (υ = 1 ← 0) at 2.8 µm clearly the best choice for sensitive detection in the infrared region by FRS. The prototype instrument shows shot-noise dominated performance and, with an active optical pathlength of only 25 cm and a lock-in time constant of 100 ms, achieves a 1σ detection limit of 8.2 × 10(8) OH radicals/cm3.

Rotational spectrum, hyperfine structure and structure of 2-azetidinone

The quadrupole hyperfine structure due to 14N in 2-azetidinone has been measured using microwave Fourier transform spectroscopy. Furthermore, the rotational constants of the 13C, 15N and 18O isotopomers have been determined permitting the calculation of the substitution structure of the heavy atom skeleton. The millimetre-wave spectrum of the main isotopomer has been measured up to 462 GHz for the ground vibrational state (Jmax = 82) as well as for the first three excited puckering states permitting the determination of accurate spectroscopic constants. High-level quantum chemical calculations of the structure have been made. The ab initio equilibrium structure is compared with the experimental structures.

Filter-free measurements of black carbon absorption using photoacoustic spectroscopy

A photoacoustic (PA) spectrophone was developed for filter-free measurement of black carbon (BC) mass absorption coefficient (MAC) in the spectral region of ~ 442 nm using a blue diode laser. The PA sensor was characterized and calibrated using NO2 at standard calibrated concentrations, as well as at indoor and outdoor air concentrations via a side-by-side intercomparison with a commercial NOx analyzer. Black carbon (graphite) and volcanic ash samples were measured under laboratory condition. MAC of BC and volcanic ash sample were determined based on the measured particles optical absorption coefficient by the PA spectrophone, in combination with the mass concentration measured using a scanning mobility particle sizer (SMPS). A minimum detectable absorption coefficient (1σ) of ~ 1.2 Mm-1 for BC was achieved with a time solution of 1 second.