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High resolution X-ray Photoelectron Spectroscopy ͑XPS͒ core-level Si 2p and O 1s spectra of the nonconductors ␣-SiO 2 ͑quartz͒ at 120 and 300 K and vitreous SiO 2 at 300 K were obtained with a Kratos Axis Ultra XPS instrument ͑instrumental resolution of Ͻ0.4 eV͒ which incorporates a unique charge compensation system that minimizes differential charge broadening on nonconductors. The Si 2p and O 1s linewidths at 300 K ͑ϳ1.1 and ϳ1.2 eV, respectively͒ are similar for all silicates ͑and similar to previous thin film SiO 2 spectra obtained previously͒, showing that differential charging does not contribute significantly to our spectra. At 120 K, there is a small decrease ͑0.04 eV͒ in the Si 2p linewidth of ␣-SiO 2 , but no measurable decrease in O 1s linewidth. The O 1s lines are generally and distinctly asymmetric. We consider all possible sources of line broadening and show that final state vibrational broadening ͑FSVB͒ and phonon broadening are the major causes of the broad and asymmetric lines. Previous high resolution gas phase XPS studies have identified large FSVB contributions to the Si 2p spectra of SiCl 4 , SiF 4 , and Si͑OCH 3 ͒ 4 molecules, and this vibrational structure leads total Si 2p 3/2 linewidths of up to ϳ0.5 eV, even with individual peak linewidths of Ͻ0.1 eV. The Si atom of Si͑OCH 3 ͒ 4 is an excellent analog for Si in crystalline SiO 2 because the Si-O bond lengths and symmetric stretch frequencies are similar in both compounds. Similar vibrational contributions to the Si 2p and O 1s spectra of solid silicates are anticipated if the Si 2p and O 1s core-hole states produce similar changes to the Si-O bond length in both phases. To investigate the possibility, Car-Parrinello molecular dynamics calculations were performed and show that changes to Si-O bond lengths between ion and ground states ͑⌬r͒ for both Si 2p and O 1s hole states are similar for both crystalline SiO 2 and gaseous Si͑OCH 3 ͒ 4 . ⌬r are −0.04 Å for Si 2p and ϳ+0.05 Å for O 1s in both compounds. Indeed, the vibrational envelope from the Si 2p spectrum of Si͑OCH 3 ͒ 4 , broadened to our instrumental linewidth of 0.4 eV, accounts for the majority ͑ϳ0.8 eV͒ of the Si 2p 3/2 linewidth for crystalline SiO 2 ͑ϳ1.1 eV͒ with phonon broadening accounting for the remainder. The results provide excellent support for the tenet that final state vibrational splitting, as seen in the gas phase molecules, similarly affects the solid-state spectra. The calculations also indicate that the O 1s linewidths should be larger than the Si 2p linewidths, as observed in our spectra. FSVB should also lead to small peak asymmetries, as seen in the O 1s spectra. The contribution of phonon broadening to the linewidth is also evaluated and shown to be comparable to the FSVB contribution at 120 and 300 K but considerably smaller at very low temperatures.

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