The weak fundamental NH-stretching transition in amines.
Absolute intensities of NH-stretching fundamental and overtone transitions of gas phase aniline, methylamine, ethylamine, cyclopropylamine, methylethylamine, diethylamine and pyrrolidine have been measured with long path length conventional absorption spectroscopy. To support the assignments of NH-stretching transitions, transition frequencies and intensities were calculated with the local mode model using ab initio calculated local mode parameters and dipole moment functions obtained at the CCSD(T)-F12a/VDZ-F12 level of theory. For aniline, the absolute intensities of the NH-stretching transitions show the typical decrease of approximately an order of magnitude for each successive vibrational excitation. For methylamine, ethylamine, cyclopropylamine, methylethylamine, diethylamine and pyrrolidine, the observed absolute intensities of the fundamental NH-stretching transition is weak and of similar strength or even weaker than the corresponding first overtone transition. Characteristic for the amines with a normal fundamental intensity is a conjugated double bond next to the amine group.
Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark.
Sidsel D
SD
Schrøder
Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark.
Anne S
AS
Hansen
Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark.
Jens H
JH
Wallberg
Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark.
Anne R
AR
Nielsen
Environment Research Institute, Shandong University, Shanda South Road 27, Jinan, Shandong, China.
Lin
L
Du
Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark. Electronic address: hgk@chem.ku.dk.
Henrik G
HG
Kjaergaard
Absolute intensity; Dipole moments; Oscillator strength; Overtones