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Definition: The steady state approximation is a method used to derive the rate law in chemical kinetics when reaction intermediates are present.
Purpose: It helps determine the concentration of short-lived intermediates that reach a steady state during chemical reactions.
The calculator uses the formula:
Where:
Explanation: The formula calculates the steady-state concentration of singlet excited state molecules considering exciplex formation and decay pathways.
Details: This approximation is crucial for understanding reaction mechanisms involving short-lived intermediates in photochemistry and other kinetic studies.
Tips: Enter the equilibrium constant (Keq), degree of exciplex formation (α, default 0.9), fluorescence rate constant (Kf, default 750 Hz), and non-radiative rate constant (KNR, default 35 Hz).
Q1: What is an exciplex?
A: An exciplex is an excited state complex formed between two different molecules that dissociates upon returning to the ground state.
Q2: What are typical values for Kf?
A: Fluorescence rate constants typically range from 106 to 109 s-1 for organic molecules.
Q3: How does α affect the result?
A: Higher α values (closer to 1) mean more exciplex formation, resulting in lower singlet state concentration.
Q4: What units should I use for Keq?
A: The calculator expects Keq in mol/m³·s. Convert from other units if necessary.
Q5: When is steady state approximation valid?
A: When the intermediate's concentration remains approximately constant during most of the reaction.