Rotational spectroscopy of transient species produced by electric discharge Electric discharges can be used to produce molecular ions, radicals, and unstable neutral molecules in the gas phase. The study of rotational spectra of molecular ions is of particular interest in relation to a possible detection of these species in the interstellar medium by radioastronomers. Rotational spectra of HN2+, HCO+, HBF+, NCCNH+, H2COH+, and SH3+ were studied in our laboratory. In particular, for the first time it has been recently observed the rotational spectrum of the molecular negative ion OD-. The same technique was also used to produce neutral species such as SO, BF, HCCF, and HCCCCF.
The J = 1 - 0 rotational transition of the molecular negative ion OD- identified thanks to the Doppler effect due to the glow discharge. [G. Cazzoli & C. Puzzarini, J. Chem. Phys. 123, 041101 (2005)]
HC17O+ (J = 1 - 0) spectrum toward the "molecular peak" of L1544 observed at IRAM 30-m antenna. The yellow line represents the hfs fit to the three hyperfine components due to the spin of the 17O nucleus. The same transition observed in laboratory producing HC17O+ by means of an electric discharge in a gaseous mixture of CH4 and 17O2 at 77 K. [L.Dore et al., Astronomy & Astrophysics 368, 712 (2001)]
Rotational spectroscopy of unstable molecules produced by gas-phase pyrolysis reactions Gas-phase, high-temperature reactions (above 1000 °C) allow for the production of unstable molecules, which can be detected using high-resolution spectroscopy techniques. Millimeter-wave spectra of phosphorus bearing compounds (HC3P, NCCP, CH3CP, HC5P, NC4P), sulphido-boron compounds (FBS, ClBS, HBS), and cyanopolyines (HC5N, HC7N) have been observed in our laboratory. Most of these species were originally detected by Kroto and coworkers in the 26-40 GHz range, but HC5P is a completely new molecule. Recording of the J = 26 - 25 rotational transition of NCCP at different pyrolysis temperatures (from 900 to 1170°C) of a gaseous mixture of PCl3 and CH3CN. This molecule has a potential interest for radioastronomical detection. [L.Bizzocchi et al., J. Chem. Phys. 113, 1465 (2000)]
Hyperfine structure investigation: the Lamb-dip technique. Rotational half-widths can be reduced by one order of magnitude by using the Lamb-dip technique. Therefore, this technique allows us to resolve hyperfine structures due to nuclear quadrupole coupling, and/or spin-rotation and/or spin-spin interactions. Thus, the Lamb-dip technique permits to very accurately determine rotational transition frequencies and parameters. Consequently, it is clear that this technique has a fundamental role in investigating molecular species of astrophysical as well as atmospherical interest. In our lab the Lamb-dip technique has been exploited for studying different isotopic sopecies of CO, HCl, HCN and NH3. Additionally, DF, HCP e PH3 have also been investigated. Hyperfine structure of the J = 1 - 0 rotational transition of H35Cl. [G. Cazzoli & C. Puzzarini, J. Molec. Spectrosc. 226, 161 (2005)] (cover picture JMS vol. 226)
Rovibrational spectroscopy and rotational spectroscopy in excited vibrational states High-resolution infrared spectra and rotational spectra in excited vibrational states yield useful information for the calculation of equilibrium structures, harmonic and anharmonic force fields. Bent and linear triatomic molecules have been investigated: FNO, ClNO, BrNO, BrCN, ICN. A small portion of the infrared spectrum of I13CN, obtained with a diode-laser spectrometer in the region of the v3 band (C-N stretch). Rovibrational lines of the fundamental band and of the four strongest hot-bands are visible. [C.Degli Esposti et al., J. Molec. Spectrosc. 182, 98 (1997)]
Lineshape analysis The physico-chemistry of the Earth’s atmosphere has been one of the main subjects of studies over last years. In particular, the composition of the atmosphere is indeed very important to understand chemical processes linked to depletion of stratospheric ozone and greenhouse effect. The vertical concentration profiles of atmospheric gases can be provided by remote sensing measurements, but they require the accurate knowledge of the parameters involved: line positions, transition intensities, pressure-broadened half-widths, pressure-induced frequency shifts and their temperature dependence. In particular, the collisional broadening parameters have a crucial influence on the accuracy of spectra calculations and on reduction of remote sensing data. Self-broadening and foreign-gas-broadening coefficients for selected rotational lines of several compounds have been determined in our lab. The molecular species investigated, some of which are interesting for atmospheric chemistry, include ClNO, CH3F, HCO+, CHF2Cl (HCFC-22), OCS, CO, CF3CFH2 (HFC-134a), O3, and HNO3. O2 broadening of the 301.8 GHz line of ozone. Frequency modulation and 2nd harmonic detection. Oxygen pressure from 40.4 mTorr (inner red trace) to 447.2 mTorr (outer blue trace). [ G. Cazzoli et al., J. Molec. Spectrosc. 229, 158 (2005) ] ESA (European Space Agency) Contract N. 16377/02/NL/FF, ESTEC (2004)

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