Vibrational predissociation spectroscopy of hydrogen-bonded complexes in the 10 micron region

Abstract

Vibrational predissociation spectroscopy of isotopomers of (CH$\sb3$OH)$\sb2$ and Ar(CH$\sb3$OH) were recorded in the 10 micron region, where the C-O stretching transition is located. Using the beam depletion technique, spectra were recorded for (CH$\sb3$OH)$\sb2$, (CH$\sb3$OD)$\sb2$,(CD$\sb3$OD)$\sb2$,(CH$\sb3$OH)(CH$ \sb3$OD),(CH$\sb3$OD)(CD$\sb3$OD),(CH$\sb3$OX)Ar (X = H,D) and (CD$\sb3$OD)Ar. It is observed that in the mixed dimers, complexes, the measured C-O transition frequencies are unchanged from their respective monomers. Time of flight measurements were also conducted to determine the translational temperature of the complexes. A band contour analysis was done to estimate the homogeneous and inhomogeneous contribution to the observed linewidths. All of the complexes except the ones containing CH$\sb3$OD methanol had a homogeneous contribution of no greater than 1 cm$\sp{-1}$. The complexes involving CH$\sb3$OD have a homogeneous width of less than 0.5 cm$\sp{-1}$. A transition dipole coupling model was studied to reveal that only 1 cm$\sp{-1}$ out of the 25 cm$\sp{-1}$ of splitting observed in (CH$\sb3$OH)$\sb2$ is due to dipole-dipole interactions. The model does not predict the isotopic shift in (CH$\sb3$OH)(CH$\sb3$OD) for either the donor or acceptor C-O stretching transition. Integral dissociation cross sections were also measured for the different species, with good agreement with a previous measurement by another group for (CH$\sb3$OH)$\sb2$. The measured integral dissociation cross sections for the various deuterated dimers decreased with the number of deuterium atoms within the complex. Preliminary studies of (CH$\sb3$NH$\sb2$)$\sb2$, Ar(CH$\sb3$NH$\sb2$), (CH$\sb3$CH$\sb2$OH)$\sb2$, Ar(CH$\sb3$CH$\sb2$OH), ((CH$\sb3$)$\sb3$COH)$\sb2$, Ar(1,4-dioxane), (1,4-dioxane)$\sb2$, Ar(d$\sb6$-acetone) and (d$\sb6$-acetone)$\sb2$ were also carried out in the 10 micron region.