Microwave spectrum, r0 structure, and ab initio calculations for trimethylphosphine

Abstract The microwave spectra of two isotopic species of trimethylphosphine, (CD 3 ) 2 (CH 3 )P and (CD 3 ) 3 P, have been recorded in the spectral region 20–39 GHz. Only c-type transitions were observed and R -branch assignments have been made for the (CD 3 ) 2 (CH 3 )P molecule and two transitions were observed for the symmetric top molecule, (CD 3 ) 3 P. From these rotational constants along with those reported for five other isotopic species of trimethylphosphine, the complete r 0 structural parameters have been determined and they are: r (PC = 1.845±0.001A, r(CH) = 1.096±0.001 A, ∠CPC = 98.95 ± 0.20°, ∠HCH = 109.02±0.16° with an angle of tilt of the methyl groups of 1.67±0.17°. The Raman spectra (3500-100 cm −1 of (CD 3 )(CH 3 ) 2 P and (CD 3 ) 2 (CH 3 )P in the liquid state have been obtained. From these data, along with the vibrational data for the d 0 - and d 9 -molecules, a complete vibrational assignment is proposed. The fundamental vibrational frequencies, barriers to internal rotation and structural parameters which have been obtained experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G basis set. Additionally, structural parameters have been calculated utilizing 3-21G * ,6-31G ** and DZ basis sets. All to these results are compared to the corresponding quantities for some similar molecules.