Vibrational Spectra and Force Constants for Isotopic Species of Nitrosyl Chloride

From infrared absorption studies in the gaseous phase, fundamental harmonic vibrational frequencies have been determined for ¹⁶O¹⁴N³⁵Cl, ¹⁶O¹⁵N³⁵Cl, ¹⁸O¹⁴N³⁵Cl, and ¹⁸O¹⁵N³⁵Cl. With the aid of centrifugal‐distortion data from the literature, a unique general quadratic valence‐force‐constant solution was obtained. The resulting values are: $F_{\mathrm{NO}}\text{\hspace{0.17em}=\hspace{0.17em}15.26}\mathrm{mdyn}{\AA }^{\text{−1}},{\mathrm{F}}_{\mathrm{NCl}}\text{\hspace{0.17em}=\hspace{0.17em}1.27}\mathrm{mdyn}{\AA }^{\text{−1}}{\mathrm{,\; F}}_{\alpha }\text{\hspace{0.17em}=\hspace{0.17em}1.32}\mathrm{mdyn}{\AA }^{\text{−1}}·{\mathrm{rad}}^{\text{−2}}{\mathrm{,\; F}}_{\mathrm{NO,NCl}}\text{\hspace{0.17em}=\hspace{0.17em}1.53}\mathrm{mdyn}{\AA }^{\text{−1}}{\mathrm{,\; F}}_{\mathrm{NO}\mathrm{,\alpha }}\text{\hspace{0.17em}=\hspace{0.17em}0.1}{\mathrm{mdyn\; rad}}^{\text{−1}}{\mathrm{,\; F}}_{\mathrm{NCl}\mathrm{,\alpha }}\text{\hspace{0.17em}=\hspace{0.17em}0.12}{\mathrm{mdyn\; rad}}^{\text{−1}}$ .