For a one-dimensional electron-phonon system we consider the photon absorption
involving electronic excitations within the pseudogap energy range. Within the adiabatic approximation
for the electron - phonon interactions these processes are described by ronlinear configurations of
an instanton type. We calculate the subgap absorption as it can be observed by means of photo
electron or tunneling spectroscopies. In details we consider systems with gapless modes: 1D
semiconductors with acoustic phonons and incommensurate charge density waves. We found that
below the free particle edge the pseudogap starts with the exponential decrease of transition rates
changing to a power law deeply within the pseudogap, near the absolute edge.
Two-dimensional chiral stacking orders in quasi-one-dimensional charge density waves