Potential energy distribution study of infrared frequencies of methylamine and methylphosphine

Normal mode assignments of the IR frequencies of methylamine and methylphosphine and their deuterated isotopomers are determined based on calculated potential energy distributions. The PED for each frequency is found using Kim’s Correspondence Rules of unified group theory and the program MOLVIB. The predominant motion of each PED is used to name the corresponding vibrational frequency. We compare our results with literature values. Our IR frequency assignments show generally good agreement with experiment and other calculations although there are some differences. We observe no differences in the principal component of normal mode PEDs across different levels of theory with the same basis set. We observe a few differences at the same level of theory with different basis sets.