Knowledge Bank

We have used current-tunable, thin-film PbTe diode lasers to obtain Doppler-limited resolution of the $v4$ band of $C3O2$ in the region 1565-1600 $cm-1$. Roughly 60% of the interval was covered using different modes of 2 lasers, each mode giving a tuning range of 1-3 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, Calibration was obtained with H$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$O and NH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$, while the frequency scale was given by the fringes of a 4-cm Ge etalon, recorded simultaneously using a double beam technique. Near 1600 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ a set of strong regularly spaced lines stands out, which is the R branch of the ground state transition. This band as wel as the ``hot” bands due to the bending vibration $v7$ indicate a linear structure for the molecule. Preliminary values in cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ for the ground state are $v0=$ 1587.392, B^{\prime\prime} - 0.07557, and B - B. This B^{\prime\prime} value differs from that reported by Lafferty et al.,$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ but agrees with that by Mantz et al.$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ The next 2 strongest series were interpretable as a $\Pi$ band with $\nu 0$ = 1580.910, B = 0.07606, B - 0.07646, B - B = 4,178 X 10$\mathrm{<mrow\; data-mjx-texclass="ORD">-4</mrow>}$, B - B = 5.259 $\times$ 10$\mathrm{<mrow\; data-mjx-texclass="ORD">-4</mrow>}$. These B values agree with Assignment 2 by Lafferty et al.$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ The assignment of the ground state transition and the shift of the “hot” bands toward lower frequency were substantiated by temperature-difference FTS spectra.