  The energy acquisition based on resonant excitations are of great importance
in chemical and biological systems. Here, the intramolecular resonant
absorption of polarized mid-infrared pulses by bulk water and surface water is
investigated using molecular dynamics simulation. The consequent heating based
on the OH stretching vibrations is found to be very prompt, achieving more than
100 K temperature jump under irradiation of a pulse with 1 ps width and maximum
intensity of 0.5 V/nm. A general anisotropic phenomenon is manifested as a
result of preferential resonant excitation of symmetric or asymmetric OH
stretching vibration, depending on the relationships between the orientations
of water molecules and the polarized direction of the pulse. In the case of
water molecules with the preferred dipole orientation, constrained by applied
static electric field or spacial confinement, parallel to the polarized
direction of the pulses, the energy absorption is dominated by the symmetric
stretching mode (around 99 THz), while in the perpendicular case, the
asymmetric stretching mode (around 101 THz) is more efficient. Since orientated
water molecules are prevalent in chemical and biological systems, these
findings concerning orientation-dependent excitation of intramolecular
vibrations are of special significance to understood the energy absorption and
transition in relevant biochemical processes.
