Determination of dissociation temperature for ArO + in inductively coupled plasma-mass spectrometry: Effects of excited electronic states and dissociation pathways

• Published in: Spectrochimica acta. Part B: Atomic spectroscopy 2011-08, Vol.66 (8), p.581-587
• Main Authors: McIntyre, Sally M., Ferguson, Jill Wisnewski, Houk, R.S.
• Format: Article
• Language: English
• Subjects: Argon oxide ion: ArO; Electron states; Excitation; Excitation spectra; Ground state; Inductively coupled plasma; Inductively coupled plasma-mass spectrometry; Ion extraction; Mathematical analysis; Origins; Spectrometry; Spectroscopy
• ISSN: 0584-8547; 1873-3565
• DOI: 10.1016/j.sab.2011.06.002

The method of comparing experimental and calculated ion ratios to determine a gas kinetic temperature (T gas) 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 T gas values. Complications arise from the predicted presence of a low-lying excited electronic state ( 2 Π) above the 4 Σ 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 2 Π excited state dissociates into Ar + and O, different products than ArO + 4 Σ 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.