PMID- 20449376
OWN - NLM
STAT- MEDLINE
DCOM- 20100811
LR  - 20131121
IS  - 1463-9084 (Electronic)
IS  - 1463-9076 (Linking)
VI  - 12
IP  - 12
DP  - 2010 Mar 28
TI  - Ionization of cytosine monomer and dimer studied by VUV photoionization and 
      electronic structure calculations.
PG  - 2860-72
LID - 10.1039/b921498d [doi]
AB  - We report a combined theoretical and experimental study of ionization of cytosine 
      monomers and dimers. Gas-phase molecules are generated by thermal vaporization of 
      cytosine followed by expansion of the vapor in a continuous supersonic jet seeded 
      in Ar. The resulting species are investigated by single photon ionization with 
      tunable vacuum-ultraviolet (VUV) synchrotron radiation and mass analyzed using 
      reflectron mass spectrometry. Energy onsets for the measured photoionization 
      efficiency (PIE) spectra are 8.60 +/- 0.05 eV and 7.6 +/- 0.1 eV for the monomer 
      and the dimer, respectively, and provide an estimate for the adiabatic ionization 
      energies (AIE). The first AIE and the ten lowest vertical ionization energies 
      (VIEs) for selected isomers of cytosine dimer computed using equation-of-motion 
      coupled-cluster (EOM-IP-CCSD) method are reported. The comparison of the computed 
      VIEs with the derivative of the PIE spectra suggests that multiple isomers of the 
      cytosine dimer are present in the molecular beam. The calculations reveal that 
      the large red shift (0.7 eV) of the first IE of the lowest-energy cytosine dimer 
      is due to strong inter-fragment electrostatic interactions, i.e., the hole 
      localized on one of the fragments is stabilized by the dipole moment of the 
      other. A sharp rise in the protonated cytosine ion (CH(+)) signal at 9.20 +/- 
      0.05 eV is ascribed to the formation of protonated cytosine by dissociation of 
      the ionized dimers. The dominant role of this channel is supported by the 
      computed energy thresholds for the CH(+) appearance and the barrierless or nearly 
      barrierless ionization-induced proton transfer observed for five isomers of the 
      dimer.
FAU - Kostko, Oleg
AU  - Kostko O
AD  - Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 
      94720, USA.
FAU - Bravaya, Ksenia
AU  - Bravaya K
FAU - Krylov, Anna
AU  - Krylov A
FAU - Ahmed, Musahid
AU  - Ahmed M
LA  - eng
PT  - Journal Article
PT  - Research Support, U.S. Gov't, Non-P.H.S.
DEP - 20100209
PL  - England
TA  - Phys Chem Chem Phys
JT  - Physical chemistry chemical physics : PCCP
JID - 100888160
RN  - 0 (Ions)
RN  - 8J337D1HZY (Cytosine)
SB  - IM
MH  - Cytosine/*chemistry
MH  - Dimerization
MH  - *Electrons
MH  - Ions/chemistry
MH  - *Light
MH  - Mass Spectrometry
MH  - Molecular Structure
MH  - Synchrotrons
MH  - Ultraviolet Rays
EDAT- 2010/05/08 06:00
MHDA- 2010/08/12 06:00
CRDT- 2010/05/08 06:00
PHST- 2010/05/08 06:00 [entrez]
PHST- 2010/05/08 06:00 [pubmed]
PHST- 2010/08/12 06:00 [medline]
AID - 10.1039/b921498d [doi]
PST - ppublish
SO  - Phys Chem Chem Phys. 2010 Mar 28;12(12):2860-72. doi: 10.1039/b921498d. Epub 2010 
      Feb 9.