On the use of variable temperature photoelectron spectroscopy studying rotational isomerism in tetramethyldiphosphine1,2

Using variable temperature photoelectron spectroscopy (VTPES), a new assignment of the UV photoelectron spectrum of tetramethyldiphosphine is derived and the equilibrium between its trans and gauche forms is quantitatively studied. The assignment is the same as those of similar hydrazines. The trans isomer is more stable than the gauche by 0.5±0.1 kcal/mol meaning that the populations of each isomer are 60% and 40% at room temperature, respectively and 50% each at 170°C. These results do not confirm the interpretation of electron diffraction data.