Simple two-pulse detection scheme in pulsed EPR for studying low-frequency nuclear coherences

Area of Science:

• * Electron Paramagnetic Resonance (EPR) Spectroscopy
• * Molecular Biophysics
• * Quantum Coherence Phenomena

Background:

• * Pulsed Electron Paramagnetic Resonance (EPR) is a powerful technique for studying paramagnetic species.
• * Detecting nuclear coherences in EPR is crucial for advanced spectroscopic analysis.
• * Instrumental dead time can limit the observation of fast-evolving coherences.

Purpose of the Study:

• * To develop and demonstrate a new method for detecting nuclear coherences in pulsed EPR.
• * To enable the immediate detection of nuclear coherences, overcoming instrumental limitations.
• * To showcase the method's applicability using a biologically relevant 15N-labeled sample.

Main Methods:

• * Employed a microwave two-pulse sequence: a weak, long 180-degree pulse followed by a hard 90-degree pulse.
• * Utilized an evolution period (T) to transfer nuclear coherences into an observable Free Induction Decay (FID).
• * Measured FID at a fixed delay after the second pulse, observing modulation with varying T.

Main Results:

• * Successfully detected nuclear coherences using the described two-pulse sequence.
• * Demonstrated that varying the evolution period (T) modulates the observed FID signal.
• * Showcased the method's ability to detect coherences immediately after their generation, avoiding dead time losses.

Conclusions:

• * The developed two-pulse EPR sequence effectively detects nuclear coherences.
• * This method allows for the immediate observation of nuclear coherences, mitigating instrumental dead time.
• * The technique is validated for studying the radical cation of 15N-labeled bacteriochlorophyll a.