Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol−Water Clusters

Kostko, Oleg; Belau, Leonid; Wilson, Kevin R.; Ahmed, Musahid

doi:10.1021/jp8020479

Cited by 45 publications

(44 citation statements)

References 37 publications

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“…As discussed earlier in literature [31,32], water and solvent clusters must thus take part in the ionization process. Water and methanol clusters have sufficiently low IEs [33,34] to be ionized by the 10.0 and 10.6 eV photons, and subsequent self-protonation can lead to generation of protonated solvent clusters. Alternatively, neutral solvent molecules can associate with dopant radical cations, and this also leads to generation of protonated solvent clusters [31].…”

Section: Ionization Of Model Compounds In Da-appimentioning

confidence: 99%

“…The solvent spectra in DA-APCI show the appearance of reagent ions at m/z 108 and 128 with increasing flow rate (Figure 2), but besides impurities, the ions could also derive from gas-phase reactions of the dopant. Another possible explanation for the decreased signals at increased flow rate could be a change in cluster size distribution: the PAs of water and methanol clusters increase with increasing cluster size [36], and IEs of methanol clusters are also smaller than for the free molecule [33,34]. Because the clusters shift to larger sizes with increasing flow rate, the clusters will effectively neutralize the dopant radical cations, and disappearance of the dopant radical cation thus prevents the charge exchange between the dopant and the analytes.…”

Section: Effect Of Flow Ratementioning

confidence: 99%

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Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

Vaikkinen

Kauppila

Kostiainen

2016

J. Am. Soc. Mass Spectrom.

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Abstract. The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M +. decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques.

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Section: Ionization Of Model Compounds In Da-appimentioning

confidence: 99%

Section: Effect Of Flow Ratementioning

confidence: 99%

Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

Vaikkinen

Kauppila

Kostiainen

2016

J. Am. Soc. Mass Spectrom.

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“…[15][16][17] This similarity suggests that it is the stability of the products, rather than the specifics of the reaction dynamics, that determines the chemical outcome. A detailed review and discussion of previous findings for both methanol and other alcohol clusters has been provided by Garvey et al…”

Section: Introductionmentioning

confidence: 99%

Electron-driven ionization of large methanol clusters in helium nanodroplets

Goulart

Bartl

Mauracher

et al. 2013

Phys. Chem. Chem. Phys.

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The electron-driven ionization of helium droplets doped with pure methanol and ethanol clusters has been investigated for the first time using high resolution mass spectrometry. Large clusters are readily accessible by this route, with up to 100 alcohol molecules seen in the present study. The mass spectra for the doped helium droplets show many similarities with previous gas phase mass spectrometric studies of methanol and ethanol clusters. Thus the dominant ion products, at least for small clusters, are

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“…A large number of experimental studies [13][14][15][16][17][18][19][20][21][22] and simulation studies [23] have been carried out in alcohol-water mixtures. Li et al [17] measured the surface concentration in the ethanol-water system by employing neutron reflection and found that the thickness and position of the ethanol layer suggests that molecules may be partially oriented with the ethyl group pointing towards the vapor phase.…”

Section: Introductionmentioning

confidence: 99%

“…Clusters in gas and condensed phases for mass spectrometric analysis were generated by several techniques. The supersonic expansion is one of the prominent methods to generate clusters, which are produced in vacuum by an expansion of sample vapor mixed with inert gas at high pressure through a nozzle [22,26]. Another method is the adiabatic expansion of a liquid jet, in which a liquid sample is directly fed to a vacuum system through an injector nozzle; in this case, the droplets explode adiabatically into high vacuum [14,15,20,21] and the clusters produced during the injection are ionized by electron ionization (EI) or photo-ionization (PI).…”

Section: Introductionmentioning

confidence: 99%

Insights on Clusters Formation Mechanism by Time of Flight Mass Spectrometry. 1. The Case of Ethanol–Water Clusters

Apicella

Passaro

2015

J. Am. Soc. Mass Spectrom.

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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 ethanolwater 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.

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Vacuum-Ultraviolet (VUV) Photoionization of Small Methanol and Methanol−Water Clusters

Cited by 45 publications

References 37 publications

Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

Electron-driven ionization of large methanol clusters in helium nanodroplets

Insights on Clusters Formation Mechanism by Time of Flight Mass Spectrometry. 1. The Case of Ethanol–Water Clusters

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