Photoinduced IR active vibrations in trans-(CD)x: a three-mode system

In a recent Letter Blanchet et al.? have extended photoinduced absorption measurements of frYms-polyacetylene to lower energy than obtained before 2 for both isotopes, (CH)x and (CD)X. While in (CE)X three strong ir-active vibrations (IRAV) are photoinduced, only two IRAV were observed in (CD)X, at ?1 = 400 cm-? and at ?2 = 1045 cm-? . This appeared strange, since from doping-induced IRAV and from resonant Raman scattering (RRS) it is known that (CD)X is also a three-mode system.3'4 Because of the asymmetry of the mode at 1045 cm'?, it was suggested that two vibrations may be contained in this line, but high-resolution examination of the line failed to resolve it. ?