65 th International Symposium on Molecular Spectroscopy June

65 th International Symposium on Molecular Spectroscopy June 24, 2010 Ohio State University Long Range Proton-Migration in VUV Photoionization of Acetone Clusters Ken-ichi Hanaue, Yoshiyuki Matsuda, Ayako Yamada, Keisuke Ohta, Naohiko Mikami, and Asuka Fujii Department of Chemistry, Graduate School of Science, Tohoku University, Japan

Cluster cations of protic molecules IR spectroscopy based on VUV photoionization detection has been applied to cluster cations of protic molecules. JCP 129, 094306 (2008). (NH 3)2+ JCP 131, 184304 (2009) (CH 3 OH)2+ PCCP 11, 1279 (2009). (CH 3 COOH)2+ VUV photoionization of protic molecular dimers intracluster H+- transfer between NH and OH Can a proton of CH (alkyl group) be transferred? Roles of solvents in VUV photoionization of solvated clusters?

This study Understanding of VUV one-photon ionization dynamics of acetone-H 2 O acetone: aprotic molecule neutral VUV photoionization cation ? ○ IR spectroscopy based on VUV photoionization detection of neutral and cationic clusters. ○ Reaction route search with the GRRM (Global Reaction Route Mapping) method

Experiment and calculation Experiment IR spectroscopy based on VUV (118 nm) photoionization detection IR spectroscopy of neutral clusters IR spectroscopy of cluster cations V’ IE dissociation Dt V’ IR S 0 ion signal IE VUV S 0 Dt dissociation IR ion signal VUV By changing the relative delaytime between of the IR and VUVpulses, IR spectroscopy of both neutral (precursor) and cationic (product) clusters in the VUV photoionization can be carried out. Calculation GRRM (Global Reaction Route Mapping) method (Maeda & Ohno, 2004) search of reaction routes following photoionization

IR spectra of neutral acetone and acetone-Ar cluster cation neutral ion signal VUV @ 128 nm acetone IE VUV MP 2/6 -31++G** Scaled by 0. 931 2800 3000 3200 3400 -1 Wavenumber / cm cation V’ IR S 0 3600 IR-VUV-PIS VUV @ 118 nm acetone+-Ar keto 16. 2 kcal/mol n. OH enol 0 kcal/mol 2600 2800 MP 2/6 -31++G** Scaled by 0. 931 3000 3200 3400 -1 Wavenumber / cm 3600 3800

IR spectra of acetone-H 2 O and (acetone-H 2 O)+ neutral acetone-H 2 O 118 nm photo -ionization detection low IR power n. CH cyclic-type cation (acetone-H 2 O)+ 2800 MP 2/6 -31++G** 3000 H-bonded n. OH 3200 3400 Wavenumber / cm-1 3600 scaled by 0. 94 118 nm photoionization H-bonded n. OH the alkyl proton migrates ! free n. OH 2600 MP 2/6 -31++G** 2800 n 1 n 3 3000 3200 3400 3600 Wavenumber / cm-1 scaled by 0. 948 3800

Proton migration mechanism proton-migration induced by photoionization VUV photoionzation cation neutral keto form enol form with the proton migration two possible mechanisms proton-relay photoionization catch & release

IR spectra of neutral and cationic acetone-D 2 O clusters neutral acetone-D 2 O free n. OD 2600 2800 catch & release n. CH 3000 3200 3400 -1 Wavenumber / cm 3600 3800 acetone-D 2 O cation no free n. OH H-bonded n. OH 2800 3000 3200 3400 Wavenumber / cm-1 3600 3800 proton-migration

Proton-migration induced by photoionization Proton-migration in ionization process catch & release catalytic action of the water molecule Calculated isomerization path in photoionization with the GRRM method PBE 1 PBE/6 -311+G(2 d, 2 p) enol II enol I

Summary IR spectroscopy based on VUV photoionization detection and reaction route search with the GRRM method were carried out to study VUV one-photon ionization dynamics of the acetone-water cluster. acetone-water VUV neutral ionization catch & release proton-migration enol type cation Intracluster proton-transfer from CH occurs upon the photoionization. The water molecule acts as the “catch & release” catalyst in the protonmigration.

apparatus Setup I TOF & DFG Ion Intensity parent ion dip spectrum IR frequency spectroscopy of neutral and cations Setup II Tandem Q-mass & IR-OPO Ion Intensity fragment ion spectroscopy of cations enhancement spectrum IR frequency

Mass spectrum of photoionization @118 nm Mass spectrum of acetone-H 2 O @118 nm (acetone)+ no higher clusters (acetone-H 2 O)+ 12 13 TOF / ms 14 15

IR spectrum of acetone-water cluster cation IRPDS-VUV-PI @118 nm (a) H+-migrated (a) H-bonded n. OH n. CH x 10 0 kcal/mol H-bonded n. OH (b) (c) Charge-shared I 26. 4 kcal/mol absorption x 10 n. CH n 1 n 3 (c) n. CH n 1 n 3 (d) n. CH n 1 n 3 (e) 2600 (e) H-transferred 33. 2 kcal/mol n. CH H-bonded n. OH free n. OH x 10 2800 3000 3200 3400 3600 Wavenumber / cm-1 Scaled by 0. 948 (b) H+-migrated II 0. 7 kcal/mol (d) Charge-shared II 29. 2 kcal/mol MP 2/6 -31++G**