J. Phys. Chem. A 2020, 124, 2505−2512

Iodization Threshold in Size-Dependent Reactions of Lead Clusters Pb_n⁺ with Iodomethane

Mengzhou Yang,^# Haiming Wu,^# Benben Huang, Zhixun Luo,^* and Klavs Hansen

* Email: zxluo@iccas.ac.cn

Abstract

Utilizing a magnetron-sputtering (MagS) source in tandem with a multiple-ion laminar flow tube (MIFT) reactor and a customized triple quadrupole mass spectrometer (TQMS), we have prepared clean Pb_n⁺ (n = 1–13) clusters and measured their reactivity with iodomethane under high carrier gas pressures. Strong size dependences are found for the reactivity of these cationic Pb_n⁺ clusters with CH₃I. For the Pb_n⁺ with n ≤ 4, iodinated clusters Pb_nI⁺ were found to be the dominant products, in strong contrast to n > 4 where no such products were seen. Quantum chemical studies show that with an increasing number of Pb atoms, the Pb–Pb interatomic interactions become stronger compared with the Pb–I bonding in Pb_nI⁺ clusters. Furthermore, the reactions of Pb_1–4⁺ with CH₃I have fairly small transition state energy barriers, in contrast to those for Pb_n>4⁺ clusters which have magnitudes that will prevent reactions under the ambient conditions.