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Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH<jats:sub>2<\/jats:sub>Cl<jats:sub>2<\/jats:sub>) doping. CH<jats:sub>2<\/jats:sub>Cl<jats:sub>2<\/jats:sub> is not a common dopant due to its high ionization energy (11.33\u2009eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6\u2009eV and was operated at ~500\u20131000\u2009Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7\u2009\u00b1\u2009122.4, 197.8\u2009\u00b1\u200918.8, 87.3\u2009\u00b1\u20097.8, and 93.5\u2009\u00b1\u200935.5 times after doping 291\u2009ppmv CH<jats:sub>2<\/jats:sub>Cl<jats:sub>2<\/jats:sub>, meanwhile CH<jats:sub>2<\/jats:sub>Cl<jats:sub>2<\/jats:sub> almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization.<\/jats:p>","DOI":"10.1038\/srep36820","type":"journal-article","created":{"date-parts":[[2016,12,1]],"date-time":"2016-12-01T11:00:58Z","timestamp":1480590058000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":26,"title":["Protonation enhancement by dichloromethane doping in low-pressure photoionization"],"prefix":"10.1038","volume":"6","author":[{"given":"Jinian","family":"Shu","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yao","family":"Zou","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ce","family":"Xu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhen","family":"Li","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wanqi","family":"Sun","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bo","family":"Yang","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Haixu","family":"Zhang","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peng","family":"Zhang","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pengkun","family":"Ma","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2016,12,1]]},"reference":[{"key":"BFsrep36820_CR1","first-page":"50","volume":"27","author":"JN Driscoll","year":"1976","unstructured":"Driscoll, J. 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