Distance measurement between trityl radicals by pulse dressed electron paramagnetic resonance with phase modulation

• Main Authors: N. Wili, H. Hintz, A. Vanas, A. Godt, G. Jeschke
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-05-01
• Series: Magnetic Resonance
• Online Access: https://mr.copernicus.org/articles/1/75/2020/mr-1-75-2020.pdf

<p>Distance measurement in the nanometre range is among the most important applications of pulse electron paramagnetic resonance today, especially in biological applications. The longest distance that can be measured by all presently used pulse sequences is determined by the phase memory time <span class="inline-formula"><i>T</i>_m</span> of the observed spins. Here we show that one can measure the dipolar coupling <i>during</i> strong microwave irradiation by using an appropriate frequency- or phase-modulation scheme, i.e. by applying pulse sequences in the nutating frame. This decouples the electron spins from the surrounding nuclear spins and thus leads to significantly longer relaxation times of the microwave-<i>dressed</i> spins (i.e. the rotating frame relaxation times <span class="inline-formula"><i>T</i>_1<i>ρ</i></span> and <span class="inline-formula"><i>T</i>_2<i>ρ</i></span>) compared to <span class="inline-formula"><i>T</i>_m</span>. The electron–electron dipolar coupling is not decoupled as long as both spins are excited, which can be implemented for trityl radicals at Q-band frequencies (35&thinsp;GHz, 1.2&thinsp;T). We show results for two bis-trityl rulers with inter-electron distances of about 4.1 and 5.3&thinsp;nm and discuss technical challenges and possible next steps.</p>