PROBING TRANS-HOOO/DOOO AND HOOO-(O$_2$)$_n$ CLUSTERS: A HENDI APPROACH

Abstract

Trans-HOOO and HOOO-(O$_2$)$_n$ clusters have been assembled in helium nanodroplets and probed with a tunable narrow linewidth PPLN-OPO laser system in the O-H stretching region. We observed the $\nu_1$ band at 3569.45 cm$^{-1}$, which consists of rotationally resolved a- and b-type components, in addition to the broad c-type $\nu_1$+$\nu_6$ band at 3699.06 cm$^{-1}$. The band origins for $\nu_1$ and $\nu_1$+$\nu_6$ are shifted to the blue by only 0.15 cm$^{-1}$ and 1.03 cm$^{-1}$, respectively, compared to the gas phase values by Lester and co-workers., 11592, (2007).}$^{,}$, 244313, (2008).} Neither of the two other predicted stable isomers, namely cis-HOOO and the hydrogen-bound OH-O$_2$ species,, 3150, (2008).} were found within a broad survey scan. The HOOO-(O$_2$)$_n$ clusters grow in to the red of the $\nu_1$ band of trans-HOOO as the O$_2$ pick-up pressure is increased. Cluster signals are resolved for up to \textit{n} $=$ 4, while signals for clusters with \textit{n} $>$ 4 pile up to form a broad feature. High level \textit{ab initio} multireference calculations are needed to help understand the geometries for these multiple O$_2$ clusters. The O-D stretch of trans-DOOO was measured at 2635.02 cm$^{-1}$, which is extremely close to the gas phase value at 2635.06 cm$^{-1}$., 9269, (2008).} The linewidths of the transitions within this band are narrower than those within the O-H stretching band of trans-HOOO, which suggests that the lifetime of the excited vibrational state is longer for trans-DOOO than trans-HOOO.