The microwave spectra of CH3CH2PH2, CH3CH2PHD, and CH3CH2PD2 have been recorded in the range 18.0 to 40.0 GHz. A-type transitions were observed and assigned for both gauche and trans conformers of ethylphosphine, and b-type transitions observed and assigned for the gauche conformer. The dipole moment components for the gauche conformer were determined from the Stark effect to be: ‖μa‖= 0.86±0.01, ‖μb‖=0.73±0.07, ‖μc‖=0.45±0.05, and ‖μt‖=1.22±0.07 D. For the trans conformers, there was only one component of the dipole moment and it had a value of ‖μa‖= ‖μt‖=1.226±0.005 D. The relative intensity of nine pairs of lines for the gauche and trans were measured at room temperature, and from the ratio of intensities it was found that ethylphosphine exists as a 45% gauche and 55% trans mixture with an energy difference of 200±100 cm−1 and the trans the more stable conformer. With reasonable assumptions for the ethyl moiety, the following structural parameters were calculated: &CCP=110.1±0.2°, rPC=1.880±0.0002 Å and PH2 dihedral angle = 61±2° and for the gauche conformer &CCP= 115.2±0.2°, rPC=1.876±0.002 Å and PH2 dihedral angle = 180±2°.

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The infrared spectra of gaseous (CH3)2CHPH2 and (CH3)2CHPD2 have been recorded from 80 to 3500 cm-1. The Raman spectra of gaseous and liquid (CH3)2CHPH2 and (CH3)2CHPD2 have been recorded from 100 to 3500 cm-1. The Raman spectrum from 100 to 3500 cm™"1 and the infrared spectrum from 450 to 3500 cm-1 of solid (CH3)2CHPH2 have been recorded. Both gauche and trans rotational isomers have been observed in the fluid phases. A vibrational assignment of the 33 normal modes has been made. Hot band transitions have been observed for the phosphino torsional mode. The average barrier to internal rotation of the methyl moiety was found to be 4.3 kcal/mol. The potential function for internal rotation around the C-P bond has been estimated. The trans conformation was found to be ~0.26 kcal/mol more stable than the gauche conformation using this estimated potential function.

The infrared spectra of gaseous and solid CH3CH2PH2 and CH3CH2PD2 have been recorded from 200 to 3500 cm−1. The Raman spectra of gaseous, liquid, and solid CH3CH2PH2 and CH3CH2PD2 have been recorded from 100 to 3500 cm−1. The gauche and trans isomers have been observed in the fluid phases and only the trans exists in the solid state. A vibrational assignment of the 24 normal modes has been made. Fundamental and hot band transitions have been observed for both the methyl and phosphino torsions. The methyl barrier in the trans d0 molecule was determined to be 3.74±0.05 kcal/mole and 3.14±0.05 for the gauche d0 molecule. The potential function for internal rotation around the C–P bond in CH3CH2PD2 was determined and the following potential constants found: V2=207±6 cm−1, V3=785±5 cm−1, and V6=−25±3 cm−1. The energy difference between the potential energy minima of the gauche and trans conformations is 150 cm−1, the trans being the more stable form. The calculated gauche–gauche barrier is 635 cm−1 (1.82 kcal/mole) and the trans–gauche barrier is 944 cm−1 (2.70 kcal/mole). A similar potential function was determined for the CH3CH2PH2 isomer but the fit to this one-dimensional model was not as good as that for the deuterium compound probably because of greater coupling in the light molecule.

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