HIGH-RESOLUTION $v_{OH}= 3\leftarrow 0$ AND $v_{OH} = 4\leftarrow 0$ OVERTONE SPECTROSCOPY OF HOD

High-resolution ($0.005 cm^{-1}$) IR overtone excitation with an injection seeded optical parametric oscillator (OPO) is used to investgate the spectroscopy of HOD in the $v_{OH} = 3\\leftarrow 0$ region via room temperature photoacoustic detection methods. Comparison of the photoacoustic spectra from an $H_{2}O/D_{2}O/HOD$ mixture and from pure $H_{2}O$ determines the lines corresponding to $v_{OH} = 3\\leftarrow 0$ absorptions in HOD. A prediction of the HOD spectrum in this region is generated from an extrapolation of $v_{OH} = 0$ and 1 rotational constants (W.S Benedict, N. Gailar, and E. K. Plyler, J. Chem. Phys. 24, 1139 (1956) and from the $v_{OH} = 3\\leftarrow 0$ band origion calculated by Tennyson and coworkers [private communication]. This predicted spectrum enables the HOD $v_{OH} = 3\\leftarrow 0$ photoacoustic spectrum to be assigned; a fit of the experimental data produces the low-order rotational constants for this transition as well as a Birge-Sponer analysis of the overtone series. The vibrational dependence of the HOD rotational constants is demonstrated to be quite linear in $v_{OH}$, permitting reliable extrapolation to the $v_{OH}$ = 4 manifold. As a result, the $v_{OH} = 0,1$ and 3 constants can be used to predict the spectrum of HOD $v_{OH} = 4\\leftarrow 0$, which now enables the assignment of the vibratrionally mediated photodissociation spectrum measured by Crim and coworkers [R. B. Metz, J. D. Thoemke, J. M. Pfeiffer, and F. F. Crim, J. Phys. Chem. 99, 1744 (1993)]. The overtone spectroscopic data for HOD is further confirmed in double resonance IR and UV photolysis of HOD and HOD-containing clusters in slit supersonic expansions.