ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
We here simulate, up to 100 ps, the conformational motion of a polymethylene molecule constrained by a cylindrical potential; the molecule is here made of 60 CH2 groups and has variable bond lengths, bond angles, and dihedral angles. We investigate the dynamical structure of the trans planar segments, especially the dihedral angle dynamics and the related twisting and out-of-plane bending motions, as a function of temperature and constraint, and we find the following: Under strong constraint, the twisting motions are dominant in the trans planar segments; the out-of-plane bending motions, however, increase with decreasing constraint resulting in a frequent generation of the gauche bonds. The dihedral angle waves propagate along the trans segments with a velocity of about 5000 m/s in two distinct series over even and odd bonds, which is a reflection of weak interactions between the adjacent dihedral angles. The overall twisting of the chain is made of local sharp twists at gauche bonds and broad gradual twists in the trans segments; the former twists are stationary, while the latter can propagate along the chain. The velocity of the latter twist is about 5000 m/s and it is almost independent of constraint. The out-of-plane bending motions, on the other hand, reflect the constraint rather sensitively. With decreasing constraint, the high frequency bending motions are greatly diminished and the velocity of the bending wave shows an appreciable slowdown. The apparently coherent annihilation and creation of the gauche bonds are often observed; the annihilation and creation occur as if they are mutually related through a dihedral angle wave.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.465908
