Adele Dell'Erba

Rotational spectrum of 1,1-difluoroethane–argon: influence of the interaction with the Ar atom on the V3 barrier to internal rotation of the methyl group

Abstract The free-jet millimeter-wave absorption spectrum of 1,1-difluoroethane–Ar is reported. Most of the measured lines are split due to internal rotation of the methyl group and the tunnelling motion of Ar connecting two equivalent potential energy minima. The Ar atom, close to the CHF 2 group, eclipses one of the methylic hydrogens in the symmetryless geometry of the complex, reducing in this way the barrier to the internal rotation of the methyl group with respect to isolated 1,1-difluoroethane. For high J levels the distance of Ar from the molecule increases, however, due to the centrifugal distortion, and the barrier increases towards the value for 1,1-difluoroethane.

Free jet rotational spectra in natural abundance of the 13C and 15N isotopic species, structures and ab initio calculations of equatorial and axial pyrrolidine ☆

Abstract The rotational spectra of all singly substituted 13 C and 15 N isotopic species of the equatorial form of pyrrolidine and all singly substituted 13 C isotopic species of the axial form have been measured in natural abundance with millimeter-wave free jet technique and r s and r 0 heavy atom geometries have been determined. Various sets of ab initio calculations give contrasting results for the energy difference between the two conformers.

Bonding energies of rare gases with aromatic molecules: rotational spectrum and dynamics of pyridazine?neon

The rotational spectrum of the pyridazine(((Ne complex, a species observable in supersonic expansions, has been measured by free jet absorption millimeter wave spectroscopy. The equilibrium configuration, dynamics and dissociation energy have been deduced from the spectroscopic constants. The equilibrium distance of Ne with respect to the center of mass of the molecule is 3.26 A, with the Ne atom tilted by 5.8° from the perpendicular to the center of mass of the ring towards the mid-point of the two nitrogen atoms. The dissociation energy is estimated, from the centrifugal distortion constant DJ, to be ca. 0.8 kJ mol?1.

Conformation of saturated seven-membered rings: free jet absorption millimeter wave spectrum of 1,3-dioxepane

Abstract The free jet millimeter wave spectrum of 1,3-dioxepane has been investigated in the 60–78 GHz frequency range. Rotational transitions belonging to the ground vibrational state have been observed and measured, yielding the rotational constants A = 3565.780(2), B = 3193.448(1) and C = 1936.312(2) MHz. The absence of low lying vibrational satellites and the kind of transitions observed (onlyμ a -type) demonstrate that, in contrast with previous reports, the molecule is rather rigid and possesses C 2 symmetry.

Investigation of a van der Waals complex with C1 symmetry: the free-jet rotational spectrum of 1,2-difluoroethane–Ar

Abstract The van der Waals complex between Ar and 1,2-difluoroethane has been investigated by free-jet absorption millimeter-wave spectroscopy in the frequency range 60–78 GHz. The analysis of the spectroscopic constants derived from the rotational spectrum allowed the determination of the dimers structure. 1,2-Difluoroethane is in the gauche conformation and the Ar atom is in a position stabilized by the interaction with one fluorine and the two carbon atoms. The distance between Ar and the center of mass (CM) of the monomer is 3.968 A, the angle between the Ar–CM line and the C–C bond is 65° and the dihedral angle Ar–CM–C–C is 99°. From centrifugal distortion effects the dissociation energy of the complex has been estimated to be 2.1 kJ/mol.

Free jet absorption millimeter wave spectrum of 2,4′-dipyridyl

Abstract The free jet millimeter wave spectrum of 2,4′-dipyridyl has been investigated in the frequency range 60–78 GHz. The two pyridine rings are tilted with respect to each other by 22.7°. Each rotational transition is split into two component lines due to the torsional motion connecting 4 equivalent minima. The lower of the two barriers to inversion, corresponding to the planar configuration, has been calculated to be 45 cm −1 .