Oriented Circular Dichroism Spectroscopy

Synonyms
OCD

Definition
Oriented circular dichroism (OCD) spectroscopy, as the name implies, is the circular dichroism spectroscopy of oriented samples. It can be a very useful technique; however, it is prone to artifacts resulting from linear dichroism contributions to the observed spectrum (Nordén et al. 2010). Thus care must be taken in collecting and analyzing the data. A sample for OCD should be symmetric about a unique orientation axis. Data must then be collected with the light propagating along that unique axis and spectra measured at different rotations about the unique axis compared. If the rotated spectra are the same, then these data can be believed. If the sample is perfectly oriented (as it would be in a perfectly oriented crystal but probably in no other method), the observed spectrum is then equivalent to three times (no rotational averaging) the CD spectrum of all the transitions in an isotropic sample except those polarized along the unique axis (which are invisible).