Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR

Abstract

1H NMR spin–lattice relaxation time measurements have been carried out in [(CH 3) 4N] 2SeO 4 in the temperature range 389–6.6 K to understand the possible phase transitions, internal motions and quantum rotational tunneling. A broad T 1 minimum observed around 280 K is attributed to the simultaneous motions of CH 3 and (CH 3) 4N groups. Magnetization recovery is found to be stretched exponential below 72 K with varying stretched exponent. Low-temperature T 1 behavior is interpreted in terms of methyl groups undergoing quantum rotational tunneling.