High-Pressure Raman and Infrared Spectroscopic Studies of Cesium Azide

Abstract

In this work, we present the effects of high pressure on the structure and stability of cesium azide (CsN 3 ) with the pressure up to ∼30.0 GPa, as studied by Raman and IR spectroscopy. Three phase transitions of Phase II → III → IV → V were revealed at ∼0.5, ∼3.7, and ∼16.0 GPa. The abnormal softening behavior of T(E g ) mode reveals the shearing distortion during Phase II → III transition. Moreover, changes of lattice modes and splitting of the degenerate T(E g ) and R(E g ) modes in Phase III indicate the breaking of crystallographically equivalent condition of azide ions. Phase IV was found to possess the C2/m structure, and Phase V has a lower symmetry structure than other phases. The IR measurements show the evolution of the NNN bending modes and the IR-active behavior of the symmetric stretch ν 1 mode under pressure, which collectively reveal the rotation and bending of the azide ions upon compression. The azide ions groups were found to further bend under pressure, and the bent azide ions might enhance propensity of nitrogen polymerization.

Effect of pressure on sodium azide studied by spectroscopic method

“…This phenomenon was also observed in previous optical and XRD studies of NaN 3 [14,26]. Moreover, the tilt angle of the azide ions was found become larger than the shear angle of the unit cell in the low temperature studies of NaN 3 [29,31,37,38]. Analogously, we speculate that the rotation angle of azide groups will become larger than the shear angle of the unit cell in the process of β-NaN 3 to α-NaN 3 .…”

“…Therefore, IR measurements are of benefit to reveal more information about azide groups of NaN 3 upon compression. Additionally, series of interesting behaviors about azide groups and phase transitional mechanism of RbN 3 , CsN 3 , and AgN 3 have revealed in our previous high-pressure IR studies [16,17,38].…”

“…This symmetric phenomenon of azide ions' bending modes has also been observed in high-pressure studies of RbN 3 , CsN 3 , and AgN 3 . Moreover, the bending behaviors in these azides are all related to the rotational behaviors of azide groups upon compression [16,17,38]. In this respect, the symmetric behavior of V 2 (A u ) and V 2 (B u ) mode of NaN 3 can attribute to the rotation of azide ions upon compression.…”

“…Therefore, more in-depth high-pressure studies about this compound are significant. Additionally, the high-pressure spectroscopic studies about azides were found to play a significant role for exploring their mechanism of phase transitions and evolution of azide ions under pressure [16,17,37,38]. Nevertheless, no experimental high-pressure IR studies about NaN 3 over these transition pressures have been reported.…”

Synthesis of 3-Acyl and 2-Acyl Imidazo [1, 2-a]pyridines by I2-Mediated Diamination of α, β-Unsaturated Ketones with 2-Aminopyridines

“…[14] In our continuing research into the synthesis of imidazo[1,2-a]pyridine derivatives, we envisioned direct diamination of α,β-unsaturated ketones with 2-aminopyridines employing molecular iodine as the sole oxidant. [15] By changing the solvent and substituents in 2-aminopyridines, 3-acyl and novel 2-acyl substituted imidazo[1,2-a]pyridine derivatives can be prepared regioselectively.…”