A FAR-WING LINE-SHAPE THEORY WHICH SATISFIES THE DETAILED BALANCE PRINCIPLE

A far-wing line shape theory in which the validity of the detailed bal ance principle is maintained in each step of the derivation is present ed. The role of the total density matrix including the initial correla tions is analyzed rigorously. By factoring out the rapidly varying ter ms in the complex-time development operator in the interaction represe ntation, better approximate expressions can be obtained. As a result, the spectral density, the Fourier transform of the dipole correlation function, can be expressed in terms of line-coupling functions in whic h two coupled lines are arranged symmetrically and whose frequency det unings are omega - 1/2(omega(ji) + omega(j'i')). Using the approximate detunings omega - omega(ji) results in expressions that do not satisf y the detailed balance principle. However, this principle remains sati sfied for the symmetrized spectral density in which not only the coupl ed lines are arranged symmetrically, but also the initial and final st ates belonging to the same lines are arranged symmetrically as well. ( C) 1998 Elsevier Science Ltd. All rights reserved.