I have some questions about applying double resonance (IR-UV, UV-UV) spectroscopy developed by Zwier's group (J. Phys. Chem. A 110(12) 4133-4150 (2006)). If we excite the conformer $A$ with photons of $E_b$ energy (under supersonically expanded circumstances, using double resonance spectroscopy), where $E_b$ is the energy barrier height of the interconversion $A\rightarrow B$, then will $A$ be converted into only the conformer $B$, or other interconversions ($A\rightarrow C$, $A\rightarrow D$, ... etc.) may take place? (In other words, if the amount of $A$, $[A]$, decreases with $\delta[A]$, then will the amount of $B$, $[B]$, increase with $\delta[A]$?) If I understand correctly, by perturbing selectively the reaction system providing $[A]_0$, $[B]_0$, $[C]_0$, and so on, initial concentrations for the species $A$, $B$, $C$, etc., the concentration changes can be followed with respect to time using double resonance spectrosopy. If no, could anybody explain me briefly how to determine the kinetic parameters using Zwier's protocol? Could we acquire the amounts of the species as a function of time for the kinetic differential equations?