Herein, we present a combined experimental and computational study of liquid phenyltrimethoxysilane. A femtosecond time-resolved optical Kerr effect experiment has been performed to study the rotational diffusion of the molecule. A new all-atoms molecular model of the compound, based on the OPLS force field, has been developed to reproduce the rotational diffusion time constant and other physical and dynamic properties available in the literature. The density obtained from the simulations is 1074 ± 4 kg m-3, which is within 1% of the experimental value of 1062 kg m-3. The viscosity from the simulations is 1.6 ± 0.1 mPa s while the experimental value is 2.1 mPa s. The average bulk dipole moment of 1.8 ± 0.5 Debye obtained from the simulation matches the experimental value of 1.77 Debye. The average relative dielectric constant from the simulations is 3.86 ± 0.04, which is within 13% of the experimental value (4.4). The rotational diffusion time of the dipole moment obtained from the simulations is 20.39 ± 0.06 ps, which is in excellent agreement with the experimental value of 20 ± 1 ps obtained from our measurements. The new model has also been used to calculate structural and dynamic properties of the molecule not yet determined experimentally.