The phase equilibrium pressure-temperature conditions in nitrogen (N-2)-tetra-n-butylammonium bromide (TBAB)-water systems (molar fractions of TBAB in aqueous solution, x(TBAB) = 0.0062, 0.0138, 0.0234, 0.0359, and 0.0529) under 1 MPa were examined using an isochoric method, and the crystal structures were assessed using the Raman spectroscopic technique. N-2-TBAB-water systems with low xTBAB (0.0062 and 0.0138) formed TBAB hydrate crystals, in contrast to the pure TBAB center dot 38H(2)O hydrate, which is the preferred crystal structure under atmospheric conditions. The TBAB hydrate crystals in low x(TBAB) showed a symmetric N-N vibrational peak of enclosed N-2 molecules at 2324.4 cm(-1). N-2-TBAB-water systems with high x(TBAB) (0.0234, 0.0359, and 0.0529) formed TBAB hydrates, similar to the pure TBAB center dot 26H(2)O hydrate. The Raman spectrum in high x(TBAB) shows an asymmetric N-N vibrational peak that can be deconvoluted into two peaks, one at 2324.2 cm(-1) and the other at 2323.7 cm(-1). These results suggest that there are two non-equivalent cages in the TBAB hydrate structure at high x(TBAB). Although other experimental techniques are required to identify these cage structures, our Raman results may provide insights into understanding TBAB hydrate structures.