Fourier transform friction mechanics

VER occurs as a result of fluctuating forces exerted by the bath on the system at the system s oscillation frequency (22). We will use the upper-case to denote the system s vibrational frequency and lower-case co to denote other vibrations. It may also be useful to look at fluctuating forces exerted on a particular chemical bond (23). Fluctuating forces are characterized by a force-force correlation function. The Fourier transform of this force correlation function at Q, denoted rj(Q), characterizes the quantum mechanical frequency-dependent friction exerted on the system by the bath (19,22). This friction, especially at higher (i.e., vibrational) frequencies, plays an essential role in condensed phase chemical reaction dynamics (24,25). 

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