The microwave spectra of 11 chemically different isotopic species of ethylphosphine (CH3CH2PH2) including all 13C and D single substituted species were recorded and assigned for the vibrational ground state. The b- and c-type transitions of the gauche conformers with symmetrically substituted ethyl groups and a PH2 group were found to be split due to tunneling between the equivalent forms. The spectra of these molecules were fit to a Hamiltonian containing Coriolis interaction terms. All other spectra were fit to asymmetric rotors with quartic centrifugal distortion. Complete rs structures were obtained for both the trans and gauche conformations. The r0 structures were derived from 45 and 48 rotational constants for the trans and gauche forms, respectively. Significant differences in the structures were found with the most notable one in the CCP angle which changes from 110.5° in the gauche form to 116° in the trans conformer. The methyl group in the gauche conformation is rotated away from a position symmetric with respect to the heavy atom plane. The structural differences are attributed to nonbonded repulsive interactions between the methyl and phosphino hydrogen atoms.
Transient laser-induced electrical signals with peak voltages of ∼50 mV and <20 ns duration (full width half-maximum) have been observed in room-temperature thin films of YBa2Cu3O7−x in the absence of an applied current. It is demonstrated that the signal polarity is reversed when the films are illuminated through the substrate rather than at the air/film interface. The mechanism for this effect has yet to be elucidated.
The microwave spectra of ethylphosphonothioic difluoride, CH3CH2P(S)F2, and eight isotopic species have been investigated in the region from 26.5 to 39.5 GHz. Only a-type transitions were observed and R-branch assignments have been made for all the isotopic species in the ground vibrational state for both the gauche and trans (methyl group trans to the P=S bond) conformers from which the rotational constants were determined. From these data the complete r0 structural parameters were determined for the gauche conformer with the values for the heavy atom parameters being: r(C–C)=1.532±0.006 Å, r(C–P)=1.800±0.007 Å, r(P=S)=1.880±0.003 Å, r(P–F)=1.555±0.005 Å, ∢CCP=112.6±0.3°, ∢CPS=119.4±0.4°, ∢CPF=102.0±0.2°, dih ∢FPCS=129.3±0.2°, and dih ∢CCPS=56.9±0.2°. The parameters of the trans conformer which differed significantly from the values for the corresponding ones in the gauche conformer were: r(C–P)=1.814±0.011 Å, r(P=S)=1.861±0.007 Å, and ∢CCP=114.8±0.2°. The infrared (3500 to 40 cm−1) and Raman (3500 to 20 cm−1) spectra of the gaseous and solid CH3CH2P(S)F2 and CD3CD2P(S)F2 as well as the Raman spectrum of the liquid have been recorded. Both trans and gauche conformers have been identified in the vibrational spectra of the fluid phases, but only the trans corformer remains in the solid state and a complete vibrational assignment is proposed for the trans conformer. The barrier to methyl rotation for the trans conformer was determined to be 808 cm−1 (2.31 kcal/mol). The asymmetric torsion for the trans conformer was observed as a series of closely spaced Q branches beginning at 73.25 cm−1 and falling to lower frequency and the gauche transitions begin at 70.82 cm−1. These transitions along with the dihedral angle for the gauche conformer have been used to obtain the potential
function for the asymmetric rotation which indicates that the trans conformer is more stable than the gauche conformer in the gas phase by 63±37 cm−1 (180±106 cal/mol). All of these results are compared with corresponding quantities for several similar organophosphorus compounds.
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