(Present Research at Toyota Riken)

Study on gas-phase NMR spectroscopy:
Preparation of cold ions in strong magnetic field and its application to gas-phase NMR spectroscopy
Toyota Physical and Chemical Research Institute, Fellow, Kiyokazu Fuke
Research background: Nuclear magnetic resonance (NMR) technique is widely used as a powerful tool to study the physical andchemical properties of materials. However, this technique is limited to the materials in condensed phases. To compensate these
problems, recently, mass spectroscopy is extensively used in broad research fields including life and medical sciences. Since thismethod essentially only gives information on the mass number, and for further chemical information computer simulations areoften required. Under these circumstances, a new extension of the NMR technique to the gas-phase molecular ions, which enable us
to obtain rich information on the structure of the target ions with a mass-spectral sensitivity, becomes increasingly important for
both fundamental and applied sciences
Principle of measurement, Progress report, and Future Plans: We proposed a new principle to detect NMR signals of gas-phasemolecular ions based on a Stern-Gerlach type experiment in a Penning-trap type cell as shown in Fig. 1.1,2 In this method, the cold
molecular ions with a slow velocity and a very narrow velocity distribution width are introduced in the cell and their magnetic
moments are probed by observing the modulation of their TOFs induced by flipping the nuclear spin with the coils placed at bothends of the cell. To realize the NMR detection, we constructed the gas-phase NMR apparatus for mass selected ions as shown in Fig.
2. We are developing the methods to prepare and manipulate cold molecular ions under the strong magnetic field. In thepreliminary experiment, the ions are cooled by four steps. A supersonic molecular beam is used to precool the neutral moleculesand photoionize it to form the cooled ion packet as cold as <2 K. Since the mean velocity of the ions is relatively high, the ionsproduced are cooled by the bunching and deceleration using a potential switch or a newly-developed traveling well potential(TPW) decelerator shown in Fig. 3. The ions decelerated are transferred to the NMR cell shown in Fig. 4 and cooled further by thevelocity selection with mesh electrodes (ca. 30 mK) and finally with a velocity dispersion compensator (< 1 mK).3 We also develop
two sets of tuned circuits including coils as shown in Fig. 4, which can operate under an ultrahigh vacuum. The coils are placed at
the higher (9.4 T) and the lower (3.1 T) homogeneous-field parts of the magnet as shown in Fig. 1 and generate two RF pulses atthe Lamor frequency of the 1H nuclei to rotate the magnetic moment by 180 degree. The two capacitors of each circuit can be
adjusted from the outside of the vacuum chamber with rotational motion feedthroughs. These coils are calibrated by measuring theNMR signal of liquid water with a FT-NMR spectrometer.
At present, we are conducting the proof-in-principle experiment. The results on the basic performance of the present apparatus
suggest that the first NMR signal for polyatomic ions will be detected in near future. We also plan to install an ion cyclotron
resonance (ICR) cell at the upstream of the NMR cell in tandem to add a mass analysis function to this apparatus
Expected results, spread effects: From a viewpoint of basic science, the present apparatus allows us to extend the NMR
measurement to the gas-phase molecular ions and to develop a new field of molecular science. By providing the mass analysis
function, the apparatus can be utilized for chemical analysis in broad fields of sciences including life and medical sciences.
References: 1) K. Fuke, et al., Rev. Sci. Instrum. 83, 085106-1-8 (2012), 2) K. Kominato, K. Fuke, et al. IEEE Trans. Appl. Supercond.,20,736 (2010). 3) K. Fuke, et al., Hyperfine Interactions, 236(1), 9-18.(2015).

Fig. 3 Ion source with multistage decelerator

Fig. 1 Schematic of gas-phase NMR apparatus
Ion source withTPW decelerator

(A)

MCP

NMR cell

8 .4

92.7
1 .6Laser(B) Field of superconductive magnet
10 1050

B (T)field (T)magnetic

Gradient field (9.4 T – 3.1 T)

5 50 0-500-50000

position(mm)
Position(mm)

50050010001000

Ion optics andelectric circuit(NMR cell; details are in Fig. 4. TPW; traveling potential well)Fig.2 Photograph of gas-phase NMR apparatus

Fig. 4 NMR cell (cooling and magnetic resonance）

RF coils (flipping magnetic moments at the cell ends)
914.8

Mesh for Front
velocity gate
selection

Velocity
dispersion
compensator

Multistage
decelerator

Back gate

Capacitors
for tuning
circuit

Magnet is 1.85 m in length and 2.2 m in height

Tuned circuit including RF coil

RF coil