Infrared Spectroscopy of the Amide I Mode of N-Methylacetamide in Solid Hydrogen at 2-4 K

We report high-resolution (0.05 cm(-1)) FTIR spectra of the fundamental and first overtone of the amide I mode of trans-N-methylacetamide (NMA) trapped in solid molecular hydrogen (SMH) at cryogenic temperatures with low (0.03%) and high (55%) ortho-hydrogen (oH(2)) concentrations. NMA-doped SMH samples with high oH(2) concentrations are nearly free from inhomogeneous broadening, permitting the measured amide I homogeneous line width of 1.268(8) cm(-1) to be used to place a lower limit on the vibrational lifetime of 4.19(3) ps. Direct observation of the amide I overtone allows the harmonic vibrational frequency omega(e) = 1726.6(5) cm-1 and the anharmonicity constant omega(e)x(e) = 8.5(2) cm(-1) to be determined for NMA isolated in SMH samples with low oH(2) concentrations.