Fourier transform infrared emission spectroscopy and ab initio calculations on RuN

The emission spectrum of RuN has been observed in the near infrared using a Fourier transform spectrometer. RuN molecules were excited in a hollow cathode lamp operated with neon gas and a trace of nitrogen. Two bands with 0–0 Q heads near 7354 and 8079 cm⁻¹ and a common lower state have been assigned as ${}^2{\Pi }_{\text{1/2}}{–}^2{\Sigma }^{+}$ and ${}^2{\Pi }_{\text{3/2}}{–}^2{\Sigma }^{+}$ subbands, respectively, of a ${\mathrm{C\hspace{0.17em}}}^2{\mathrm{\Pi –X\hspace{0.17em}}}^2{\Sigma }^{+}$ transition. A rotational analysis of these bands has been performed and molecular constants have been extracted. The principal molecular constants for the ground ${\mathrm{X\hspace{0.17em}}}^2{\Sigma }^{+}$ state of the most abundant ${}^{\mathrm{102}}\mathrm{RuN}$ isotopomer are: $B_0\text{=0.552\hspace{0.17em}782\hspace{0.17em}9(70)\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}},$ $D_0{\text{=5.515(13)×10}}^{\text{−7}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}},$ ${\gamma }_0$ $\text{=−0.044\hspace{0.17em}432(22)\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}$ and $r_0\text{=1.573\hspace{0.17em}869(10)\hspace{0.17em}Å.}$ The excited ${\mathrm{C\hspace{0.17em}}}^2\Pi$ state has the following molecular constants: $T_{00}\text{=7714.342\hspace{0.17em}60(53)\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}},$ $A_0\text{=725.8064(11)\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}},$ $B_0\text{=0.516\hspace{0.17em}843\hspace{0.17em}4(80)\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}},$ $D_0{\text{=5.685(16)×10}}^{\text{−7}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}},$ $p_0{\text{=5.467(36)×10}}^{\text{−3}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{-1}}$ and $r_0\text{=1.627\hspace{0.17em}670(13)\hspace{0.17em}Å.}$ Ab initio calculations have been carried out on RuN to ascertain the nature of the experimentally observed states and to predict the spectroscopic properties of the low-lying electronic states. Our electronic assignment is supported by these calculations and is also consistent with the observations for the isoelectronic RhC molecule [Kaving and Scullman, J. Mol. Spectrosc. 32, 475–500 (1969)]. The valence electron configuration ${\text{1σ}}^2{\text{2σ}}^2{\text{1π}}^4{\text{1δ}}^4{\text{3σ}}^1$ is proposed for the ${\mathrm{X\hspace{0.17em}}}^2{\Sigma }^{+}$ ground state of RuN and the configurations for the excited states have been discussed. There is no previous experimental or theoretical work on RuN.