Electron-electron-ion triple-coincidence experiment of electron-initiated valence ionization of small water clusters

The ionization and fragmentation of small water clusters induced by electron impact (80 eV) is investigated. Using a multiparticle coincidence spectrometer (reaction microscope), all three charged final state particles—two outgoing electrons and one fragment ion—are detected. Nonprotonated <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msubsup><a:mrow><a:mo>(</a:mo><a:msub><a:mi mathvariant="normal">H</a:mi><a:mn>2</a:mn></a:msub><a:mi mathvariant="normal">O</a:mi><a:mo>)</a:mo></a:mrow><a:mn>2</a:mn><a:mo>+</a:mo></a:msubsup></a:math> and protonated water clusters <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msub><d:mi mathvariant="normal">H</d:mi><d:mn>3</d:mn></d:msub><d:msup><d:mrow><d:mi mathvariant="normal">O</d:mi></d:mrow><d:mo>+</d:mo></d:msup></d:mrow><d:mo>,</d:mo><d:mo> </d:mo><d:mrow><d:msub><d:mrow><d:mo>[</d:mo><d:msub><d:mi mathvariant="normal">H</d:mi><d:mn>2</d:mn></d:msub><d:mi mathvariant="normal">O</d:mi><d:mo>]</d:mo></d:mrow><d:mn>2</d:mn></d:msub><d:msup><d:mrow><d:mi mathvariant="normal">H</d:mi></d:mrow><d:mo>+</d:mo></d:msup></d:mrow><d:mo>,</d:mo><d:mo> </d:mo><d:mrow><d:msub><d:mrow><d:mo>[</d:mo><d:msub><d:mi mathvariant="normal">H</d:mi><d:mn>2</d:mn></d:msub><d:mi mathvariant="normal">O</d:mi><d:mo>]</d:mo></d:mrow><d:mn>4</d:mn></d:msub><d:msup><d:mrow><d:mi mathvariant="normal">H</d:mi></d:mrow><d:mo>+</d:mo></d:msup></d:mrow></d:math>, and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:mrow><m:msub><m:mrow><m:mo>[</m:mo><m:msub><m:mi mathvariant="normal">H</m:mi><m:mn>2</m:mn></m:msub><m:mi mathvariant="normal">O</m:mi><m:mo>]</m:mo></m:mrow><m:mn>5</m:mn></m:msub><m:msup><m:mrow><m:mi mathvariant="normal">H</m:mi></m:mrow><m:mo>+</m:mo></m:msup></m:mrow></m:math> are identified in the measured ion spectrum. The ionization channels for formation of these species are investigated by measuring the kinetic energy distributions and the electronic states of the ions. Only a single state can lead to (<q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:mrow><q:msub><q:mi mathvariant="normal">H</q:mi><q:mn>2</q:mn></q:msub><q:msubsup><q:mrow><q:mi mathvariant="normal">O</q:mi><q:mo>)</q:mo></q:mrow><q:mn>2</q:mn><q:mo>+</q:mo></q:msubsup></q:mrow></q:math>, which is identified as ionization of water dimer with a <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mrow><t:mn>1</t:mn><t:msub><t:mi mathvariant="normal">b</t:mi><t:mn>1</t:mn></t:msub></t:mrow></t:math> hole at the hydrogen bonding donor molecule, while for the protonated water species three major electronic states corresponding to the ionization of <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:mrow><v:mn>1</v:mn><v:msub><v:mi mathvariant="normal">b</v:mi><v:mn>1</v:mn></v:msub></v:mrow><v:mo>,</v:mo><v:mo> </v:mo><v:mrow><v:mn>3</v:mn><v:msub><v:mi mathvariant="normal">a</v:mi><v:mn>1</v:mn></v:msub></v:mrow></v:math>, and <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"><y:mrow><y:mn>1</y:mn><y:msub><y:mi mathvariant="normal">b</y:mi><y:mn>2</y:mn></y:msub></y:mrow></y:math> type orbitals are observed. Published by the American Physical Society 2024