|
Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. December 2002, Volume 1, Number 12, 636-658 |
A Simple Predictive Model for Molecular Vibrations of Polycyclic
Aromatic Hydrocarbons: An Extended Version of the MO/8 Model
Koichi Ohno, Risako Takahashi, Megumi Yamada, and Yumiko Isogai
Internet Electron. J. Mol. Des. 2002, 1, 636-658
|
Abstract:
Polycyclic aromatic hydrocarbons (PAHs) are interesting targets of
studies in connection with astrophysics of intersteller medium,
molecular engineering of electronic devices, and environmental and
biological chemistry of toxicity and carcinogenicity. Since topological
connections between carbon atoms play decisive roles in properties of
PAHs, we present a simple predictive model for molecular vibrations of
PAHs with no additional information other than its topology, which can
be applied to any size of PAHs without modification. The force field
model is expressed in a quadratic form with valence internal coordinates.
Conjugation effects of π electrons on the collective motions of electrons
and nuclei in the carbon networks are included in the force constants for
CC bond stretchings by using π electron bond-orders (BO) and
bond-bond polarizabilities (BBP). This model previously developed as MO/8
is considerably improved as an extended version MO/8E to be used for
both even and odd alternant PAHs and also for their excited states and
ionic states. The MO/8E model is developed on the basis of Hückel and
semiempirical molecular orbital methods. Ground-state molecular
vibrations of PAHs can be predicted for both planar and out-of-plane
modes for any size of PAHs with the accuracy of ca. 20 cm-1.
Excited-state vibrations can also be predicted in the accuracy of ca.
30 cm-1. The computation time of the MO/8E model
is much smaller (10-5)
than DFT and ab initio calculations. The MO/8E model is efficient in
predicting molecular vibrations of PAHs with
20 cm-1 (30 cm-1)
accuracy for ground (excited) states without any data except for
topological connections of hexagonal rings. MO/8 models will be
released at the following address:
http://qpcrkk.chem.tohoku.ac.jp./koukai/WMO8/WebMO8_Eng.HTM
|