Variable path-length liquid cells for infrared spectros-copy are items of routine application. The literature contains few, if any, references to their gas-phase counterpart, however. One obvious use for a variable path-length gas cell would be as a reference cell for the cancellation of the background spectra of gases during <i>in situ</i> studies of weak adsorption on sample dises of varying thickness.
Ronald L. Musselman and Charles P. Nash, "A Variable Path-Length Infrared Gas Cell," Appl. Spectrosc. 29, 527-528 (1975)