Knowledge Bank

Thirty-four transitions in the $\nu 3$ (asymmetric stretch) fundamental of the azide anion have been measured in an $NH3/N2O$ discharge using diode laser velocity modulation spectroscopy. The data, ranging from P(42) to R(62), were fit to a linear molecule effective Hamiltonian quartic terms. The vibrational band origin was determined to be $\nu 3=1986.4672(19)cm-1$ and the rotational constants are $B\prime \prime =.426203(57)cm-1$ and $B\prime \prime =.422572(55)cm-1$. Comparisons with ab initio calculations and condensed phase measurements are presented. The observed 2:1 intensity alternation in successive rotational lines establishes the centrosymmetric structure of the anion ($r0=1.188402(82)A)$.