Knowledge Bank

High resolution IR spectroscopy of (HCCCN)$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ and HCCCN-HCN systems was investigated in this work. Both the inner and outside C-H stretching mode were studied. The structures of both dimers are determined to be linear. The van der Waals bendlengths were determined fat both molecules. The center of the $v1$ dimer band of the HCCCN dimer is $2.95cm-1$ red shifted from that of the monomer band, while the $v2$ band center is red shifted by $67cm-1$. In the region of the inside C-H stretching band (the $v2$ band) of the HCCCN dimer, two bands were observed with $0.8cm-1$ away from each other. The source of the weaker band in not clear. One possibility is that is a hot band. This is interesting because the linewidths for the weaker band transitions are narrower than that of the strong band lines, while in usual case one would expect that the linewidth of the hot band transitions should be at least as broad as those of the cold band $transitions.1$ The stronger band transitions have a linewidth of 295 MHz, which corresponds to a predissociation liftime of 530 ps, while the linewidth of the weaker band lines is about 190 MHz, corresponding to a predissociation lifetime of 825 ps. It in also possible that the weaker band is due to an anharmonic vibrational perturbation.