title: Insights on Clusters Formation Mechanism by Time of Flight Mass Spectrometry. 1. The Case of Ethanol-Water Clusters.
abstract: In the present work, water clusters with the addition of an electrophilic molecule such as ethanol have been studied by time of flight mass spectrometry (TOFMS). Mass distributions of molecular clusters of ethanol, water, and ethanol-water mixed clusters were obtained by two different ionization methods: electron ionization (EI) and picosecond laser photo-ionization (PI) at a wavelength of 355 nm. It was shown that short pulse laser ionization increases the signal intensity and promotes the extension of the detected mass range of the clusters in comparison with EI. Much larger clusters were detected in our experiments with respect to the current literature. The autocorrelation function (AF) was introduced in the analysis of the composition of the water clusters in terms of fundamental periodicities for obtaining information on clusters formation mechanisms. Besides, it was found that ethanol molecules are capable of substitutional interaction with hydrogen-bonded water clusters in ethanol-water binary mixtures but the self-association of ethanol was the dominant process. Moreover, the increase of ethanol concentration promotes both the formation of hydrated ethanol clusters and the self-association of ethanol clusters in ethanol-water binary mixtures. The formation of water-rich clusters and subsequent metastable fragmentation were found to be the dominant processes determining the water-rich cluster distribution, irrespective of the ionization process, while the ionization process significantly affects the ethanol-rich cluster distribution.
authors.affiliation: Istituto di Ricerche sulla Combustione, IRC-CNR, P.le Tecchio 80, 80125, Napoli, Italy.|Key Laboratory of Power Machinery and Engineering, Ministry of Education, Shanghai Jiao Tong University, Shanghai, 200240, China.
authors.forename: Xinling
authors.initials: X
authors.lastname: Li
authors.affiliation: SPIN - CNR, Via Cintia, 80124, Napoli, Italy.
authors.forename: Xuan
authors.initials: X
authors.lastname: Wang
authors.affiliation: Istituto di Ricerche sulla Combustione, IRC-CNR, P.le Tecchio 80, 80125, Napoli, Italy.|Chemical Engineering, Materials and Industrial Production Department, University of Naples Federico II, P.le Tecchio 80, 80125, Napoli, Italy.
authors.forename: Maria dell'Arco
authors.initials: Md
authors.lastname: Passaro
authors.affiliation: CNISM and Physics Department, University of Naples Federico II, Via Cintia, 80124, Napoli, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Spinelli
authors.affiliation: Istituto di Ricerche sulla Combustione, IRC-CNR, P.le Tecchio 80, 80125, Napoli, Italy. apicella@irc.cnr.it.
authors.forename: Barbara
authors.initials: B
authors.lastname: Apicella
keywords: Ethanol–water clusters; Photo-ionization; Reflectron time-of-flight mass spectrometry; Short-pulse laser