UV photodissociation of α-alanine was studied by parahydrogen matrix isolation infrared spectroscopy. The temporal behavior of Fourier transform infrared spectra revealed that UV irradiation at 213 nm yielded the HOCO radical as a direct photoproduct from the S 2 excited state. The concentration of HOCO quickly approached a steady state due to secondary photodissociation of HOCO to produce CO 2 + H or CO + OH. On the other hand, no photoproducts were detected by S 1 excitation at 266 nm. Irradiation of fully deuterated α-alanine at 213 nm yielded ∼2 times more cis-DOCO radicals than the lower energy isomer trans-DOCO, indicating that the conformation of the hydroxyl group is fairly well-preserved upon photodissociation of α-alanine. The present study suggests that HOCO may be a good tracer species in the search for amino acids in interstellar space.
Amino
acids are the building blocks of proteins, and their detection
in outer space thus has implications on the origin of life. They form
a zwitterionic structure in aqueous environments while adopting a
neutral configuration in the gas phase. We perform an experimental
and computational study on the number of water molecules needed for
zwitterion formation of β-alanine. Our density functional theory
investigation reveals that a minimum of five water molecules are required
to form and stabilize the zwitterion. A characteristic connecting
water molecule located between the COO– and NH3
+ groups is found
to enhance the stability. This water molecule is also involved in
a characteristic infrared active vibration at ≈1560 cm–1, which is slightly shifted with the number of surrounding
water molecules and is located in a spectral region outside of water
vibrations. A corresponding infrared signal is found in high-resolution
experimental spectra of β-alanine and water in a solid para-hydrogen
matrix.
Samples of H2O, HDO, and D2O were isolated in solid parahydrogen (pH2) matrices and irradiated by vacuum ultraviolet (VUV) radiation at 147 nm. Fourier-Transform Infrared (FTIR) spectra showed a clear...
With
the use of solid parahydrogen in matrix isolation spectroscopy
becoming more commonplace over the past few decades, it is increasingly
important to understand the behavior of molecules isolated in this
solid. The mobility of molecules in solid parahydrogen can play an
important role in the dynamics of the system. Water molecules embedded
in solid parahydrogen as deposited were found to be mobile at 4.0
K on the time scale of a few days. The diffusion at this temperature
must be due to quantum tunneling in solid parahydrogen. The diffusion
dynamics were analyzed based on the theory of nucleation. The concentration
dependence on the diffusion rate indicates that there might be correlated
motion of water molecules, a signature of quantum diffusion. We find
that both water monomers and water dimers migrate in solid parahydrogen
and provide insight into the behavior of molecules embedded in this
quantum crystal.
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