Determination of dissociation temperature for ArO in inductively coupled plasma-mass spectrometry: Effects of excited electronic states and dissociation pathways |
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Authors: | Sally M. McIntyre Jill Wisnewski Ferguson R.S. Houk |
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Affiliation: | aAmes Laboratory U.S. Department of Energy, Department of Chemistry, Iowa State University, Ames, IA 50011, USA |
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Abstract: | The method of comparing experimental and calculated ion ratios to determine a gas kinetic temperature (Tgas) characteristic of the origin of a polyatomic ion in inductively coupled plasma-mass spectrometry (ICP-MS) is applied to ArO+. Repeated measurements of ion ratios involving this species yield erratic Tgas values. Complications arise from the predicted presence of a low-lying excited electronic state (2Π) above the 4Σ ground state. Omission of this excited state yields unreasonably high temperatures (> 10,000 K) for nine out of nineteen trials. Inclusion of the excited electronic state in the partition function of ArO+ causes temperatures to increase further. The problem appears to be related to the prediction that ArO+ in the 2Π excited state dissociates into Ar+ and O, different products than ArO+ 4Σ which dissociates into Ar and O+. Adjustments to the calculations to account for these different products yield reasonable temperatures (2100 to 3500 K) that are consistent from day-to-day and similar to those seen for other weakly-bound polyatomic ions. |
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Keywords: | Inductively coupled plasma-mass spectrometry Inductively coupled plasma Ion extraction Argon oxide ion: ArO+ |
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