Fig. 2.

Gas phase NMR spectra collected at 11.7 T of ¹²⁹Xe (A and B) and ¹³¹Xe (C and D). Also indicated are the associated energy levels at thermal, high temperature equilibrium (A and C) and after optical pumping using the transition Δ_m = −1 (B and D). (A) ¹²⁹Xe NMR spectrum of xenon at 400 kPa (partial pressure) of pure xenon and 100 kPa (partial pressure) oxygen using 250 transients. (B) Hyperpolarized ¹²⁹Xe NMR spectrum with 10 kPa (partial pressure) xenon from a 200 kPa, 5% xenon gas mixture after a single stopped-flow delivery. Note that the scale of (A) is threefold enlarged compared to (B) in this figure. (C) Thermal ¹³¹Xe NMR spectrum after 1260 transients with a partial pressure of 93 kPa of xenon from a 100 kPa, 93% xenon gas mixture and (D) hyperpolarized ¹³¹Xe NMR spectrum after a single stopped-flow delivery using 10 kPa xenon partial pressure of a 200 kPa, 5% xenon gas mixture. The scale of (D) is 10-fold enlarged compared to (C). All hyperpolarized spectra are collected with one transient. When correcting for xenon partial pressures and number of transients, enhancements of 33,000 (corresponding to 37% spin polarization) and 1500 (i.e. 0.8% spin polarization) were achieved for ¹²⁹Xe and ¹³¹Xe, respectively. Note, that up to 2.2% ¹³¹Xe spin polarization was obtained in later experiments shown in Fig. 4. The differences in the relative phase are due to the positive gyromagnetic ratio of ¹³¹Xe, as discussed in Section 3.3. All spectra were recorded using xenon with natural abundance isotope distribution.