Knowledge Bank

The (0,0) band of the $A~3\Pi u-X~3\Sigma g+$ transition of NCN, observed previously by Herzberg and Travis , has been reinvestigated by means of laser-induced fluorescence at 329 nm. A frequency doubled dye laser was used to record the spectrum of NCN downstream of a microwave discharge through $N2$ and $CF4$ in $Heb$. From the rotational analysis, improved values for the molecular constants of NCN in both states were obtained, including A-type doubling parameters for the $3\Pi$ upper state.The main molecular constants obtained were $$ \tilde{X}^{3}\Sigma^{+}{g}:\qquad B^{\prime\prime}{000}=0.3972458(95) \mbox{ cm }^{-1}\qquad X^{n}=0.79402(50)\mbox{ cm}^{-1} $$ $$ \tilde{A}^{3}\Pi_{u}^{+}:\qquad B^{\prime}{000}=0.3966487(95)\mbox{cm}^{-1}\qquad A^{\prime}=37.4493(38)\mbox{cm}^{-1} $$ $$ T^{\prime}{000}=30388.8110(51)\mbox{cm}^{-1} $$ THE $B$ values (and hence bond lengths) are very similar in the two states and therefore the spectrum is dominated by $\Delta t=0$ transitions. The (010)-(010) band occurs in a similar wavelength region, the excited state of this transition exhibiting the Renner-Teller effect. Analyses of both the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Delta g-3u\Pi$ and the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma g-3\Pi u$ components of this hot band will be presented.