Intermolecular proton-transfer in acetic acid clusters induced by vacuum-ultraviolet photoionization

Abstract

Infrared (IR) spectroscopy based on vacuum-ultraviolet one-photon ionization detection was carried out to investigate geometric structures of neutral and cationic clusters of acetic acid: (CH(3)COOH)(2), CH(3)COOH-CH(3)OH, and CH(3)COOH-H(2)O. All the neutral clusters have cyclic-type intermolecular structures, in which acetic acid and solvent molecules act as both hydrogen donors and acceptors, and two hydrogen-bonds are formed. On the other hand, (CH(3)COOH)(2) (+) and (CH(3)COOH-CH(3)OH)(+) form proton-transferred structures, where the acetic acid moiety donates the proton to the counter molecule. (CH(3)COOH-H(2)O)(+) has a non-proton-transferred structure, where CH(3)COOH(+) and H(2)O are hydrogen-bonded. The origin of these structural differences among the cluster cations is discussed with the relative sizes of the proton affinities of the cluster components and the potential energy curves along the proton-transfer coordinate.

Experimental and theoretical investigations of isomerization reactions of ionized acetone and its dimer

“…11 Therefore, ionization dynamics of molecules and clusters can be effectively investigated by this spectroscopy. [11][12][13] Ionization dynamics of clusters sheds new light on ion-molecule reactions and intermolecular processes following various ionization such as electron impact, chemical ionization, and matrix-assisted laser desorption/ionization. Molecular level investigations of ionization dynamics of clusters would elucidate detailed mechanisms of these processes.…”

“…We have clarified that the photoionized clusters form the proton-transferred structures, in which the protonated cation is hydrogen (H)-bonded to the counter radical, i.e., NH 2 , CH 3 O, and CH 3 COO, respectively. 11,13,[20][21][22] These protontransferred structures are formed through the intermolecular proton-transfer between the hydrophilic groups without an effective energy barrier following the ionization. 11,13,[20][21][22][23][24][25] Generation of protonated species is also observed in ionization of clusters of aprotic molecules such as ketones, ethers, and amines.…”

“…11,13,[20][21][22] These protontransferred structures are formed through the intermolecular proton-transfer between the hydrophilic groups without an effective energy barrier following the ionization. 11,13,[20][21][22][23][24][25] Generation of protonated species is also observed in ionization of clusters of aprotic molecules such as ketones, ethers, and amines. [26][27][28][29][30][31] Their generation would be explained by protontransfer from alkyl groups following the ionization.…”

Mass-selected IR-VUV (118 nm) spectroscopic studies of radicals, aliphatic molecules, and their clusters

“…Taking acetic acid dimer cations as the example, six stable conformers (VI + − I + ) were found by optimizing at PBEPBE/6‐311 + G(2d,2p) level (Guan et al, ). Matsuda et al (Ohta et al, ) using the IRPDS‐VUV‐PI technique finds that structures V + and IV + are the dominant structures for (CH 3 COOH) 2 + irradiated by 10.5 eV photons. Two fragments, the protonated ions (CH 3 COOH) n −1 H + and the fragment ions (CH 3 COOH) n −1 –COOH + , are considered to be related to the same neutral cluster precursor.…”

Unraveling the Mechanisms of the Excited‐State Intermolecular Proton Transfer (ESPT) for a D‐π‐A Molecular Architecture

“…As one of the most fundamental processes and the vital roles in ab road range of chemical and biological processes (including acid-base reactions, solution dynamics, ionization dynamics, photoexcitation dynamics, and physiologicalf unctions), [1][2][3][4][5] the excited-state proton transfer, which can be classifiedi nto excited-state intramolecular proton transfer (ESIPT) and excited-state intermolecularp roton transfer( ESPT), has received considerable attentionsi nt he past severald ecades, and remained an activet opic among researchersb oth theoretically and experimentally. [6][7][8][9][10] The unique photophysical and photochemicalp roperties of the ESPT/ESIPT (especially the large Stokes-shifted emission) have endowed them potentiala pplications in al arger number of fields, such as laser dyes, organic optoelectronic materials, molecular probes (detecting polarity, pH, viscosity,a nd ions), white-light-emitting materials,p hos-phorescent-emitting materials, ando pticali nformation storage materials. [11][12][13][14][15][16] Hence,t he search for new chromophores with excellent ESPT/ESIPT properties and fundamental understanding of the mechanism of ESPT/ESIPT are of both theoretical and practical value, because their functionality or physicochemicalactivity may be protonation-state sensitive.…”