Longitudinal acoustical accordion modes LAMs

LAMs were first observed in the low-frequency Raman spectra of solid n-alkanes as strong, polarised bands with frequency inversely proportional to the chain length [243]. They are due to a symmetrical accordon-like vibration of the extended chain, which can be modelled as an elastic rod of modulus E, length L and density p, with a resultant vibrational frequency Elp)il2L. Therefore, the effect of chain length on frequency is predicted by a simple mechanical model. 

A different LAM mode, termed the disorder or D-LAM, has also been observed at higher ( 200cm ) frequencies in a range of polymers [251,258,259]. This mode appears to be associated specifically with confor-mationally disordered regions and bears the familiar inverse dependence upon region size. 

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LAM Longitudinal acoustic type (or accordion like) mode in alkanes. 

The longitudinal acoustic mode (LAM) is found in a number of semicrystalline polymers. The LAM mode for the all-trans -alkanes is a symmetric accordion-like... 

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