Negative Ion Photoelectron Spectra of Deprotonated Benzonitrile Isomers via Computation of Franck-Condon Factors

Rebecca A Firth; Taylor L Dimino; Wilson K Gichuhi

doi:10.1021/acs.jpca.2c03220

Negative Ion Photoelectron Spectra of Deprotonated Benzonitrile Isomers via Computation of Franck-Condon Factors

J Phys Chem A. 2022 Jul 28;126(29):4781-4790. doi: 10.1021/acs.jpca.2c03220. Epub 2022 Jul 18.

Authors

Rebecca A Firth¹, Taylor L Dimino^{1

2}, Wilson K Gichuhi¹

Affiliations

¹ Department of Chemistry, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States.
² Department of Chemical Engineering, Tennessee Tech University, 1 William L. Jones Dr., Cookeville, Tennessee 38505, United States.

PMID: 35849483
DOI: 10.1021/acs.jpca.2c03220

Abstract

Negative ion photoelectron spectra of ortho (o-), meta (m-), and para (p-) deprotonated benzonitrile (o-, m-, p-C₆H₄(CN)^-) isomers as well as the associated thermochemical values corresponding to deprotonation at o-, m-, and p-positions in C₆H₅(CN) are presented. Quantum mechanical results based on the density functional theory (DFT) utilizing the aug-cc-pVQZ basis set indicate that the o-, m-, p-C₆H₄(CN)^● radicals have electron affinity values (EAs) of 1.901, 1.778, and 1.789 eV, respectively. The computed Franck-Condon (FC) factors give rise to o-, m-, and p-C₆H₄(CN)^- negative ion spectra with FC active ring distortion vibrational modes with harmonic vibrational frequencies of ∼450, 760, and 1000 cm^-1 as the dominant vibrational progressions. Deprotonation at the o-, m-, and p-positions in C₆H₅(CN) results in calculated gas-phase acidity values (Δ_acidH_298K^o) of 383.9, 385.7, and 385.3 kcal mol^-1, respectively. The calculated Δ_acidH_298K^o is in close agreement with the previously reported high-pressure mass spectrometry experimental value of 383.4.0 ± 4.4 kcal mol^-1. The computed Δ_acidH_298K^o and EAs are utilized to estimate the bond dissociation energy (DH₂₉₈(H-C₆H₄CN)) associated with the formation o-, m-, and p-C₆H₄(CN)^● using the negative ion thermochemical cycle: DH₂₉₈(C₆H₅CN) = Δ_acidH_298K^o (H-C₆H₄(CN) + EA (C₆H₅CN)^● - IP(H). The respective values of DH₂₉₈(H-C₆H₄CN) corresponding to the formation of ortho, meta, and para C₆H₄(CN) radicals are 114.15, 113.11, and 113.51 kcal mol^-1.