Using the high-resolution pulsed field ionization-photoelectron (PFI-PE) and PFI-PE-photoion coincidence (PFI-PEPICO) techniques, we have examined the formation of methyl cation from the dissociation of energy-selected (X=Br and I) near their dissociation thresholds. The breakdown diagrams for thus obtained yield values of 12.834±0.002 eV and 12.269±0.003 eV for the 0 K dissociative threshold or appearance energy (AE) for from and respectively. Similar to the observation in PFI-PE studies of and the PFI-PE spectrum for exhibits a step at the 0 K AE for indicating that the dissociation of excited in high-n (⩾100) Rydberg states at energies slightly above the dissociation threshold occurs in a time scale of The observed step is a confirmation of the 0 K from determined in the PFI-PEPICO study. The adiabatic ionization energies (IEs) for the spin–orbit states were determined by PFI-PE measurements to be 10.5427±0.0010 and 10.8615±0.0010 eV, respectively, yielding the spin–orbit coupling constant to be 2571±4 cm−1. The values from and and the value obtained here, when combined with the known IE of (9.8380±0.0004 eV) and (9.5381±0.0001 eV), have allowed accurate determination of the 0 K bond dissociation energies for (2.996±0.002 eV), (2.291±0.002 eV), (2.431±0.003 eV), and (2.731±0.003 eV). Using the from and together with the known 0 K heats of formation for Br (117.93±0.13 kJ/mol), I (107.16±0.04 kJ/mol), and (1099.05±0.33 kJ/mol), we have obtained more precise values for (−21.30±0.42 kJ/mol) and (22.43±0.50 kJ/mol). This experiment demonstrated that highly reliable values for a range of molecules with error limits comparable to those for some of the most precisely measured values, such as can be obtained by PFI-PE and PFI-PEPICO measurements.
High-resolution energy-selected study of the reaction Accurate thermochemistry for the (X=Br, I) system
Y. Song, X.-M. Qian, K.-C. Lau, C. Y. Ng, Jianbo Liu, Wenwu Chen; High-resolution energy-selected study of the reaction Accurate thermochemistry for the (X=Br, I) system. J. Chem. Phys. 1 September 2001; 115 (9): 4095–4104. https://doi.org/10.1063/1.1391268
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