Observation of the Low-Frequency Spectrum of the Water Dimer as a Sensitive Test of the Water Dimer Potential and Dipole Moment Surfaces.

Using the helium nanodroplet isolation setup at the ultrabright free-electron laser source FELIX in Nijmegen (BoHeNDI@FELIX), the intermolecular modes of water dimer in the frequency region from 70 to 550 cm were recorded. Observed bands were assigned to donor torsion, acceptor wag, acceptor twist, intermolecular stretch, donor torsion overtone, and in-plane and out-of-plane librational modes. This experimental data set provides a sensitive test for state-of-the-art water potentials and dipole moment surfaces.

The FELion cryogenic ion trap beam line at the FELIX free-electron laser laboratory: infrared signatures of primary alcohol cations.

The combination of a 4 K 22-pole ion trap instrument, FELion, with the widely tunable free electron lasers at the FELIX Laboratory is described in detail. It allows for wide-range infrared vibrational spectroscopy of molecular ions. In this study, the apparatus is used for infrared vibrational predissociation (IR-PD) measurements of the simple alcohol cations of methanol and ethanol as well as their protonated forms.

Tilting after Dutch windmills: probably no long-lived Davydov solitons in proteins.

We present a summary of picosecond pump-probe and photon echo experiments in the mid-IR at 6 mum on the protein myoglobin. The intriguing temperature dependence of the amide I band in Mb is rather similar to the temperature dependence of the amide I band of acetanilide, the molecule that launched Al Scott down the road of looking for Davydov solitons in biology. Alas, after much effort, we believe the data show that there is no long-lived Davydov soliton, at least in myoglobin.

Picosecond thermometer in the amide I band of myoglobin.

The amide I and II bands in myoglobin show a heterogeneous temperature dependence, with bands at 6.17 and 6.43 microm which are more intense at low temperatures.

Charge-state resolved mid-infrared spectroscopy of a gas-phase protein.

Infrared spectra of a 104 amino-acid protein in the gas phase as a function of its charge state are presented. The spectra contain clearly resolvable bands in the amide I and II spectral regions, as well as a band at 1483 cm(-1), which is not observed in solution phase spectroscopy and is especially prominent for the higher charge states. Compared to solution, the amide I band is blue-shifted and the amide II band red-shifted, as expected for species in an environment with reduced hydrogen bonding.

Ultrafast vibrational dynamics and stability of deuterated amorphous silicon.

Infrared four-wave mixing experiments performed upon deuterated amorphous silicon layers (a-Si:D) reveal profound differences in the dynamics of Si-D stretch vibrations compared to those of analogous Si-H vibrational modes in hydrogenated amorphous silicon (a-Si:H). Remarkably, transient-grating measurements of the population decay rate of the Si-D vibrations show single-exponential decay directly into collective modes of the a-Si host, bypassing the local bending modes of the defect into which the Si-H vibrations decay. Photon-echo measurements of the vibrational dephasing suggest at low temperature contributions from TO nonequilibrium phonons and at elevated temperatures elastic phonon scattering of TA phonons.