The molecular organization at the aqueous DMSO and MSA surfaces has been investigated using vibrational 
sum frequency generation (VSFG) spectroscopy and molecular dynamics (MD) simulations. The molecular 
orientation of surface DMSO and MSA is deduced based on the VSFG spectra of both C-H stretch and 
S-O stretch regions. The S-O stretch region is studied for the first time and is shown to be critical 
in molecular orientation determination. On average, the CH3 groups of DMSO and MSA are preferentially 
pointing outwards into the air. However, the DMSO S=O group points slightly inwards away from the surface, 
while the SO3 vector of dissociated MSA pointing nearly straight down. In addition, MD simulations reveal 
that the orientation distribution of surface DMSO is relatively broad in contrast with a narrow distribution 
of surface MSA, which agrees with the experiment findings.