Microwave spectrum of gauche-isopropylphosphine

The microwave spectra of isopropylphosphine has been recorded in the region 12.4–40.0 GHz. Both a- and b-type transitions were observed and assigned. The rigid rotor rotational constants were determined to be A = 7633.34 ± 0.09, B = 4243.36 ± 0.02, and C = 3045.84 ± 0.02 MHz for (CH₃)₂CHPH₂ and A = 7226.47 ± 0.05, B = 4041.06 ± 0.02, and C = 2946.85 ± 0.02 MHz for (CH₃)₂CHPD₂. Dipole moment components of |μ_a| = 1.15 ± 0.01, |μ_b| = 0.43 ± 0.01, |μ_c| = 0.03 ± 0.02 and |μ_t| = 1.23 ± 0.01 were determined from the Stark effect. From the microwave spectra, the Stark effect and the experimental rotational constants, the assigned spectrum has been identified to result from the gauche form and this conformer is believed to be more stable than the other form which is present at room temperature.