Mass Spectrometric Determination of the Heats of Atomization of NdO2, NdBO, and NdBO2 and Upper Values for the Dissociation Energies of NdAg and Nd2

During evaporation of Nd and Ag from a boron nitride Knudsen cell the new molecules NdO_2(g), NdBO_(g), and NdBO_2(g) were detected by mass spectrometric analysis. The enthalpies of the following reactions were determined by a third‐law method: $${\mathrm{NdO}}_{\text{2(g)}}+{\mathrm{Nd}}_{\mathrm{(g)}}\text{→2}{\mathrm{NdO}}_{\mathrm{(g)}}{\mathrm{,\; \Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}10.5\hspace{0.17em}±\hspace{0.17em}1.2}{\mathrm{kcal\; mol}}^{\text{−1}},$$ $${\mathrm{NdBO}}_{\mathrm{(g)}}\to {\mathrm{Nd}}_{\mathrm{(g)}}+{\mathrm{BO}}_{\mathrm{(g)}}{\mathrm{,\; \Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}77.4\hspace{0.17em}±\hspace{0.17em}1.9}{\mathrm{kcal\; mol}}^{\text{−1}},$$ $${\mathrm{Nd}}_{\mathrm{(g)}}+{\mathrm{NdBO}}_{\text{2(g)}}\to {\mathrm{NdBO}}_{\mathrm{(g)}}+{\mathrm{NdO}}_{\mathrm{(g)}}{\mathrm{,\; \Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}10.5\hspace{0.17em}±\hspace{0.17em}4.}{\mathrm{kcal\; mol}}^{\text{−1}}.$$ From these reaction enthalpies the heats of atomization of NdO₂, NdBO, and NdBO₂ were calculated: ${\mathrm{NdO}}_{\text{2(g)}}{\mathrm{:\; \Delta H}}_0{°}_{\mathrm{atom}}\text{\hspace{0.17em}=\hspace{0.17em}323.5\hspace{0.17em}±\hspace{0.17em}12.5}{\mathrm{kcal\; mol}}^{\text{−1}};{\mathrm{NdBO}}_{\mathrm{(g)}}{\mathrm{:\; \Delta H}}_0{°}_{\mathrm{atom}}\text{\hspace{0.17em}=\hspace{0.17em}268.7\hspace{0.17em}±\hspace{0.17em}10}{\mathrm{kcal\; mol}}^{\text{−1}};{\mathrm{NdBO}}_{\text{2(g)}}{\mathrm{:\; \Delta H}}_0{°}_{\mathrm{atom}}\text{\hspace{0.17em}=\hspace{0.17em}446.2\hspace{0.17em}±\hspace{0.17em}13}{\mathrm{kcal\; mol}}^{\text{−1}}$ . A discussion of the possible geometric arrangement of these molecules on the basis of thermochemical data is given. Upper limits for the bond energies of Nd_2(g) and NdAg_(g) are given as 39 and 50 kcal mol⁻¹, respectively.