A spectral analysis based on the concept of a global phase map derived from generalized two-dimensional (2D) synchronous and asynchronous correlation spectra has been applied to actual experimental data to demonstrate its potential. As an application of a global 2D phase map, temperature-dependent infrared transmission spectra from 30 to 80°C of an eleven-layer Langmuir-Blodgett (LB) film of 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (dodecyl-TCNQ) have been investigated. Although the generalized 2D correlation asynchronous map presents only a very weak signal due to the CH3 asymmetric stretching vibration compared with much stronger signals due to the CH2 stretching vibrations of dodecyl-TCNQ, the global 2D phase map clearly shows the distinct nonlinear response arising from the CH3 asymmetric stretching vibration. The detection of nonlinear responses suggests that the active thermal movement of the alkyl-chain loses a trans-zigzag skeleton plane in the intermediate state above 80°C between the solid and melt states.
- Generalized two-dimensional correlation spectroscopy
- Langmuir-Blodgett films
- Phase angle
- Temperature-dependent infrared spectra