The CH3PH2 and CH3PH isomers: isomerization, hydrogen release, thermodynamic, and spectroscopy properties

In this study was performed a quantum chemical investigation of the methylphosphine molecule and its radical, which may show potential implications in interstellar processes, and may be crucial atmospheric tracer gasses in the atmosphere of Giant planets. The analyses were performed with the density functional theory and coupled cluster methods. The anharmonic vibrational modes were predicted for all the isomers. The atomic charge distribution was analyzed with different methodologies and some methods fail to establish the correct sign for phosphorous atom charges. The CH2PH2/CH3PH and CHPH3/CH3PH energy gap is 16.45-17.43 and 67.05-69.02 kcal mol(-1), respectively. The CH2PH3/CH3PH2 energy difference ranges from 44.62 to 50.05 kcal mol(-1). The ionization energy predicted with the W1BD method for CH3PH and CH3PH2 are 8.73 and 9.01 eV, respectively. The heat of formation at 298 K for each molecule were calculated in kcal mol(-1): CH3PH (24.16-25.27), CH2PH2 (41.20-42.47), CHPH3 (92.50-94.23), CH3PH2 (-4.73-2.83) and CH2PH3 (40.03-42.55). The rotational energy barriers for CH3PH2 and CH2PH3 are 1.65 and 2.81 kcal mol(-1), respectively. The CHPH3→CH2PH2 unimolecular arrangement presents a barrier energy of 29.89 kcal mol(-1), whereas CH3PH→CH2PH2 is accessible overcoming a barrier of 42.42 kcal mol(-1). The H2-release routes for CH2PH2 from carbon and phosphorous atoms show a barrier of 98.19 and 46.67 kcal mol(-1), respectively. For the CH3PH2→CH2PH3 isomerization, an energy barrier of 94.00 kcal mol(-1) was predicted, while for the H2-release pathway for CH3PH2 it is necessary to pass a potential energy barrier of 97.56 kcal mol(-1).