I have a question regarding the limitations of Electron Spin Resonance (ESR). I've read somewhere that ESR cannot detect radicals with short lifetimes. I'm trying to understand what exactly is meant by that. For example: a highly dynamic system like liquid sulfur at high temperatures (350 °C). Sulfur chains with two radical chain-ends are constantly reacting with other sulfur molecules at an average rate of every 100 picoseconds. Will ESR be able to detect any signal in this case? Even though radicals are fast to react, we have a steady-state concentration of radicals (on average radical concentration remains the same). I would really appreciate any paper regarding this.
In highly dynamic systems like liquid sulfur at high temperatures, Electron Spin Resonance (ESR) may face limitations in detecting radicals with short lifetimes. The fast reactivity and constant reactions every 100 picoseconds could result in a transient nature of the radicals, making them challenging to capture with ESR. The technique is more effective for stable radicals with longer lifetimes.
In your case, where there's a steady-state concentration of radicals despite their fast reactivity, ESR might still detect a signal, but the challenge lies in the transient nature of the radicals. To delve deeper into this topic, you may find relevant information in scientific literature on ESR and radical dynamics in high-temperature sulfur systems. Look for studies on ESR applications in dynamic environments or radical systems with short lifetimes for a more detailed understanding of these limitations.
Tehmina Khan
Thank you very much for your reply.
- All the papers I've found mention that it's impossible to detect short-lived radicals with ESR, but they don't provide detailed explanations.
- Basically, the issue isn't about the steady-state concentration but about the transient nature of short-lived radicals.
- This might be a naive question, but how exactly is the lifetime of a radical defined? Is it from initiation to termination, or can every step in the propagation reaction be considered the end of life of the radical?
I would greatly appreciate if you have any relevant litterature to share.
Kind regards
The difficulty in detecting short-lived radicals with Electron Spin Resonance (ESR) lies in their transient nature, as you mentioned. The lifetime of a radical is indeed a critical factor in this context.
The lifetime of a radical is typically defined from its initiation to termination. It spans the entire period during which the radical exists as an intermediate species in a chemical reaction. The initiation step produces the radical, and the termination step marks the end of its existence as a separate species.
In the context of propagation reactions, each step in the reaction sequence contributes to the overall lifetime of the radical. However, it's essential to note that the concept of radical lifetime can vary depending on the specific reaction and the conditions under which it occurs.
The challenge with short-lived radicals in systems like liquid sulfur at high temperatures is that their existence may be very brief, making it difficult to capture and observe them using techniques like ESR, which may require longer-lived radicals for effective detection. The transient nature of these radicals might not provide a sufficient window for detection before they undergo further reactions or termination steps.
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