Effects of mixing between short-chain and branched-chain alcohols in protonated clusters

• Published in: Physical chemistry chemical physics : PCCP 2020-06, Vol.22 (23), p.13223-13239
• Main Authors: Hsu, Po-Jen, Shinkai, Takahiro, Tai, Pei-Han, Fujii, Asuka, Kuo, Jer-Lai
• Format: Article
• Language: English
• Subjects: Butanol; Chain branching; Chains; Clusters; Computer simulation; Density functional theory; Dispersion; First principles; Hydrogen bonding; Infrared spectroscopy; Isomers; Spectrum analysis; Temperature dependence
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp01116a

The previous analysis of the neat protonated branched-chain alcohol clusters revealed the impact of steric repulsion and dispersion of the bulky alkyl group on the hydrogen-bonded (H-bonded) structures and their temperature-dependence. To further understand the influence of the alkyl groups in H-bonded clusters, we studied the mixing of the two extremes of alcohols, methanol (MeOH) and tert -butyl alcohol ( t -BuOH), with an excess proton. Infrared spectroscopy and a structural search of first principles calculations on the size-selected clusters H + (MeOH) m ( t -BuOH) t ( m + t = 4 and 5) were conducted. Temperature-dependence of the dominant H-bonded structures was explored by the Ar-tagging technique and quantum harmonic superposition approach. By introducing the dispersion-corrected density functional theory methods, it was shown that the effects of dispersion due to the bulky alkyl groups in the mixed clusters cannot be ignored for t ≥ 2. The computational results qualitatively depicted the characteristics of the observed IR spectra, but overestimation of the temperature-dependence with dispersion correction was clearly seen due to the unbalanced correction between linear H-bonded structures and compact cyclic ones. These results demonstrate the importance of extensive investigation and benchmarks on different levels of theory, and that a properly sampled structure database is crucial to evaluate theoretical models. The temperature-dependence and hydrogen-bonded structures of protonated methanol and tert -butyl alcohol mixed clusters were explored by using size-selective infrared spectroscopy and an extensive structure search using density functional theory.