PMID- 17500546
OWN - NLM
STAT- MEDLINE
DCOM- 20070928
LR  - 20131121
IS  - 1089-5639 (Print)
IS  - 1089-5639 (Linking)
VI  - 111
IP  - 31
DP  - 2007 Aug 9
TI  - Vibrational spectroscopy of protonated imidazole and its complexes with water 
      molecules: ab initio anharmonic calculations and experiments.
PG  - 7374-81
AB  - The results of anharmonic frequency calculations on neutral imidazole (C3N2H4, 
      Im), protonated imidazole (ImH+), and its complexes with water (ImH+)(H2O)n, are 
      presented and compared to gas phase infrared photodissociation spectroscopy 
      (IRPD) data. Anharmonic frequencies are obtained via ab initio vibrational 
      self-consistent field (VSCF) calculations taking into account pairwise 
      interactions between the normal modes. The key results are: (1) Prediction of 
      anharmonic vibrational frequencies on an MP2 ab initio potential energy surface 
      show excellent agreement with experiment and outstanding improvement over the 
      harmonic frequencies. For example, the ab initio calculated anharmonic frequency 
      for (ImH+)(H2O)N2 exhibits an overall average percentage error of 0.6% from 
      experiment. (2) Anharmonic vibrational frequencies calculated on a semiempirical 
      potential energy surface fitted to ab initio harmonic data represents 
      spectroscopy well, particularly for water complexes. As an example, anharmonic 
      frequencies for (ImH+)H2O and (ImH+)(H2O)2 show an overall average deviation of 
      1.02% and 1.05% from experiment, respectively. This agreement between theory and 
      experiment also supports the validity and use of the pairwise approximation used 
      in the calculations. (3) Anharmonic coupling due to hydration effects is found to 
      significantly reduce the vibrational frequencies for the NH stretch modes. The 
      frequency of the NH stretch is observed to increase with the removal of a water 
      molecule or replacement of water with N2. This result also indicates the ability 
      of the VSCF method to predict accurate frequencies in a matrix environment. The 
      calculation provides insights into the nature of anharmonic effects in the 
      potential surface. Analysis of percentage anharmoncity in neutral Im and ImH+ 
      shows a higher percentage anharmonicity in the NH and CH stretch modes of neutral 
      Im. Also, we observe that anharmonicity in the NH stretch modes of ImH+ have some 
      contribution from coupling effects, while that of neutral Im has no contribution 
      whatsoever from mode-mode coupling. It is concluded that the incorporation of 
      anharmonic effects in the calculation brings theory and experiment into much 
      closer agreement for these systems.
FAU - Adesokan, Adeyemi A
AU  - Adesokan AA
AD  - Department of Chemistry, University of California at Irvine, Irvine, California 
      92697, USA.
FAU - Chaban, Galina M
AU  - Chaban GM
FAU - Dopfer, Otto
AU  - Dopfer O
FAU - Gerber, R Benny
AU  - Gerber RB
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PT  - Research Support, U.S. Gov't, Non-P.H.S.
DEP - 20070515
PL  - United States
TA  - J Phys Chem A
JT  - The journal of physical chemistry. A
JID - 9890903
RN  - 0 (Imidazoles)
RN  - 0 (Macromolecular Substances)
RN  - 0 (Protons)
RN  - 059QF0KO0R (Water)
SB  - IM
MH  - *Algorithms
MH  - Energy Transfer
MH  - Imidazoles/*chemistry
MH  - Macromolecular Substances/chemistry
MH  - *Protons
MH  - Spectrum Analysis
MH  - Thermodynamics
MH  - *Vibration
MH  - Water/*chemistry
EDAT- 2007/05/16 09:00
MHDA- 2007/09/29 09:00
CRDT- 2007/05/16 09:00
PHST- 2007/05/16 09:00 [pubmed]
PHST- 2007/09/29 09:00 [medline]
PHST- 2007/05/16 09:00 [entrez]
AID - 10.1021/jp070785w [doi]
PST - ppublish
SO  - J Phys Chem A. 2007 Aug 9;111(31):7374-81. doi: 10.1021/jp070785w. Epub 2007 May 
      15.