On the vibrations of N2O trapped in solid para-hydrogen

The spectroscopy of molecules trapped in para-hydrogen (p-H2) matrix revealed unique properties of the quantum solid environment. But it has been limited to the low-lying vibrational states while we believe the investigations on the highly excited states may provide new viewpoint of such interesting system. Here we report the infrared spectroscopy of nitrous oxide in solid para-hydrogen in the 1000-7000 cm−1 region. Fourteen bands including very high overtones like 5ν1 were assigned for each of the three isotopologues of N2O: N142O16, N14N15O16, and N15N14O16. All these observed N2O/p-H2 bands are found red-shifted. The relative intensity of the 5ν1 band in solid hydrogen matrix was found to be about 100 times higher than that in the gas phase which implies anomalous enhancement by the matrix environment. We also observed “anomalous” high-resolution structures in the ν3, ν1+ν3 and 2ν3 bands of N2O/p-H2. The multiple peaks in the subtle band structures were found regularly separated, temperature-dependent and reversible. The simulation reveals a 142 cm−1 high barrier between different orientations of the N2O molecule in the p-H2 matrix. The barrier can be accounted for by the hours-long relaxation revealed from the spectra observed at 4.3 K. According to the characters of the observed spectral features, we conclude that the multiple peaks may originate from the multiple orientations of the N2O molecules isolated in the p-H2 matrices. It can also interpret that why some bands are with spreading structures while others are just significantly broadened.