Editing Ionization (section)

===Multiphoton ionization of inner-valence electrons and fragmentation of polyatomic molecules===
The ionization of inner valence electrons are responsible for the fragmentation of polyatomic molecules in strong laser fields. According to a qualitative model<ref>{{cite journal|url=http://slchin-symposium.copl.ulaval.ca/MPublication/168_CPL_313_0789.pdf |doi=10.1016/S0009-2614(99)01075-1 |title=Multiphoton ionization of inner-valence electrons and fragmentation of ethylene in an intense Ti:sapphire laser pulse |date=1999 |last1=Talebpour |first1=A. |last2=Bandrauk |first2=A. D. |last3=Yang |first3=J |last4=Chin |first4=S. L. |journal=Chemical Physics Letters |volume=313 |issue=5–6 |page=789 |bibcode=1999CPL...313..789T |url-status=dead |archive-url=https://web.archive.org/web/20141121115050/http://slchin-symposium.copl.ulaval.ca/MPublication/168_CPL_313_0789.pdf |archive-date=November 21, 2014 }}</ref><ref>{{cite journal|doi=10.1088/0953-4075/33/21/307|title=Dissociative ionization of benzene in intense ultra-fast laser pulses|date=2000|last1=Talebpour|first1=A|last2=Bandrauk|first2=A D|last3=Vijayalakshmi|first3=K|last4=Chin|first4=S L|journal=Journal of Physics B: Atomic, Molecular and Optical Physics|volume=33|issue=21|page=4615|bibcode=2000JPhB...33.4615T |s2cid=250738396 }}</ref> the dissociation of the molecules occurs through a three-step mechanism:
*MPI of electrons from the inner orbitals of the molecule which results in a molecular ion in ro-vibrational levels of an excited electronic state;
*Rapid radiationless transition to the high-lying ro-vibrational levels of a lower electronic state; and
*Subsequent dissociation of the ion to different fragments through various fragmentation channels.

The short pulse induced molecular fragmentation may be used as an ion source for high performance mass spectroscopy. The selectivity provided by a short pulse based source is superior to that expected when using the conventional electron ionization based sources, in particular when the identification of optical isomers is required.<ref>{{cite journal|doi=10.1007/s00340-008-3038-y|title=Ultra-fast laser pulses provide an ion source for highly selective mass spectroscopy|journal=Applied Physics B|volume=91|issue=3–4|pages=579|year=2008 |last1=Mehdi Sharifi |first1=S. |last2=Talebpour |first2=A. |last3=Chin |first3=S. L.| bibcode=2008ApPhB..91..579M| s2cid=122546433}}</ref><ref name="PengPuskas2012">{{cite journal |last1=Peng |first1=Jiahui |last2=Puskas |first2=Noah |last3=Corkum |first3=Paul B. |last4=Rayner |first4=David M.|last5=Loboda |first5=Alexandre V. |title=High-Pressure Gas Phase Femtosecond Laser Ionization Mass Spectrometry |journal=Analytical Chemistry |volume=84 |issue=13 |date=2012 |pages=5633–5640 |issn=0003-2700 |doi=10.1021/ac300743k|pmid=22670784|s2cid=10780362 |url=https://nrc-publications.canada.ca/eng/view/accepted/?id=8c0691b7-362f-4e8b-bc8f-39e7fc7b6c62 }}</ref>