Zero electron kinetic energy photoelectron and threshold photoionization spectroscopy of M-X(CH₃)₃ (M= Ga, In; X = P, As)

This paper presents pulsed-field ionization, zero electron kinetic energy (ZEKE) photoelectron and threshold photoionization spectra of M-X(CH ₃)₃ (M = Ga, In; X = P, As). The ZEKE spectra exhibit well-resolved vibrational structures. A comparison with B3LYP calculations shows that the spectrum of In-P(CH₃)₃ arises from the ¹A₁ ← ²E transition and the spectra of Ga-P(CH₃)₃ and Ga-As(CH₃)₃ arise from transitions of a Jahn-Teller distorted doublet state to the ¹A₁ state. The intensities of the 1A ₁-²E transition in the indium species are described with the Franck-Condon approximation, while the transitions in the gallium complexes are more complicated due to the dynamic Jahn-Teller effect. The adiabatic ionization potentials of Ga-P(CH₃)₃, In-P(CH ₃)₃, and Ga-As(CH₃)₃ are 39 635, 38 930, and 40 322 cm^-1, respectively, and the ionization threshold of In-As(CH₃)₃ is ∼39 550 cm^-1. The metal-ligand stretching frequencies are 143, 116, and 125 cm^-1 for Ga⁺-P, In⁺-P, and Ga⁺-As. respectively, and 96 cm^-1 for In-P. The intermolecular bending frequencies are 71, 65, and 42 cm^-1 for Ga⁺-P-C, In⁺-P-C, and Ga ⁺-As-C, respectively, and 47 cm^-1 for In-P-C. In addition, ligand-based vibrational frequencies are determined for the CH₃ wag, PC₃ and AsC₃ umbrella, and P-C stretching vibrations.