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CHN hydrogen bond formation in trimethylamine dimer upon one-photon ionization Yuichiro Nakayama, Yoshiyuki Matsuda, and Asuka Fujii Department of Chemistry, Graduate School of Science, Tohoku University, Japan

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Introduction Most stable cation NeutralProton-migration VUV photoionization Matsuda et al. Angew. Chem. Int. Ed. 49, 4898 (2010) Keto-enol tautomerization in the VUV photoionization of the acetone-water cluster Proton-migration from a methyl group Does a cationic alkyl group act as proton donor and/or H-bond donor? A neutral alkyl group generally does not act as a proton donor

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This study Understand the ability of the cationic methyl group as H-bond donor Aim Exp. & Calc. IR spectroscopy of (TMA) 2 and (TMA) 2 + through the VUV photoionization detection Theoretical calculations of structures, harmonic vibration, and potential energy curves of the cationic state Trimethylamine (TMA) dimer cation TMA has only the methyl groups and nitrogen. Sample

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Experiment IRPDS-VUV-PI (IR Predissociation Spectroscopy of VUV-Pumped Ion) VUV-ID-IRPDS (VUV-Ionization-Detected IR Predissociation Spectroscopy) Matsuda et al. Phys. Chem. Chem. Phys. 11, 1265 (2009) IR spectroscopy for neutral clusters IR spectroscopy for cationic clusters We can observe IR spectra of both neutral and cationic clusters

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IR spectrum of neutral (TMA) 2 The most stable structure VUV-ID-IRPDS

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IR spectrum of (TMA) 2 + A broad H-bonded X-H stretch band is observed

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Energy Diagram of the reaction of (TMA) 2 + AIE (CH-N) H + -transfer-type I Most stable Zero point energy 1.3 kcal/mol Vertically ionized structure Energy (kcal/mol) Intrinsic Reaction Coordinate ( 1/2 ) AIE (C-HN) H-bond-type Coexistence of two structures

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Isomerization reaction of (TMA) 2 induced by photoionization A proton is shared between C and N A methyl group acts as a hydrogen-bond donor in the cationic state VUV One-photon ionization NeutralCation

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Summary VUV One-photon ionization NeutralCation We observed the IR spectra of (TMA) 2 and (TMA) 2 + with spectroscopies based on the VUV photoionization detection. We calculated the isomerization reaction potential energy curve following the one-photon ionization. In the VUV photoionization process, (TMA) 2 is isomerized to the structure in which a proton is shared between C and N. In this structure, the methyl group acts as the proton donor.

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IR spectrum of (TMA) 2 + IRPDS-VUV-PI