Inelastic X-ray Scattering of a Transition-Metal Complex (FeCl₄^–): Vibrational Spectroscopy for All Normal Modes

Abstract

The tetraethylammonium salt of the transition metal complex (FeCl4−) has been examined using inelastic x-ray scattering (IXS) with 1.5 meV resolution (12 cm−1) at 21.747 keV. This sample serves as a feasibility test for more complex transition metal complexes. The IXS spectra were compared with previously recorded infrared, Raman, and NRVS spectra, revealing the same normal modes but with less strict selection rules. Calculations with a previously derived Urey Bradley force field were used to simulate the expected Q and orientation dependence of the IXS intensities. The relative merits of IXS, as compared to other photon based vibrational spectroscopies such as NRVS, Raman, and IR are discussed.

A time-correlation function approach to nuclear dynamical effects in X-ray spectroscopy

“…[4,5] In Ref. 6, RIXS has been even regarded to be a complementary technique to the conventional vibrational infra-red and Raman spectroscopies. Although X-ray scattering processes occur during few femtoseconds due to the typically short lifetimes of core-excited states, indications of ultrafast nuclear dynamics could be observed.…”

Nuclear Resonance Vibrational Spectroscopy: A Modern Tool to Pinpoint Site-Specific Cooperative Processes

“…Meanwhile, the NRVS signal (lifetime on the order of nanoseco be well separated from the electronic scattering (lifetime on the order of femtosec the time domain. Thus, NRVS does not need to extract the signal from backgrou low-throughput diffraction spectrometer, such as in the case of inelastic X-ray s (IXS) [50,51]. The time domain distinction makes NRVS spectra have highe [FeFe] hydrogenase (a1) and its reaction center (H-cluster, six irons) (a2).…”

“…All the dedicated NRS beamlines have HRM and NRVS measurement separated in different hutches to prevent the temperature surge around HRMs due to beam on and off activities. A positive aspect is that the temperature sensitivity can sometimes be intentionally used as a mechanism of tuning monochromator energy instead of rotating θ; for example, the backscattering HRM for IXS experiments at Spring-8 BL35XU uses such a mechanism to scan Si (11,11,11) around 21.8 keV with~1.5 meV resolution [50,51]. However, this alternative type of HRM is not used for NRVS.…”

“…Meanwhile, the NRVS signal (lifetime on the order of nanoseconds) can be well separated from the electronic scattering (lifetime on the order of femtoseconds) in the time domain. Thus, NRVS does not need to extract the signal from background via a low-throughput diffraction spectrometer, such as in the case of inelastic X-ray scattering (IXS) [ 50 , 51 ]. The time domain distinction makes NRVS spectra have higher signal throughput, an almost zero background, and with a true zero wave number (cm −1 ) start, which in turn makes the measurement on extremely weak (0.1 counts per seconds or 0.1 cts/s) signal possible, such as the Fe–H–Ni vibrational peak [ 7 , 8 ] in Figure 1b .…”

Non-equilibrium x-ray spectroscopy using direct quantum dynamics

“…Indeed, RXES can achieve the spectral resolution (∼50 meV) required to go beyond electronic transitions and resolve individual vibronic and vibrational energy levels. [16][17][18][19][20][21][22] Importantly, the resonant nature of RXES means that the intermediate core-hole states involved in the second-order process have a finite lifetime, which have been harnessed to study ultrafast (<10 fs) nuclear 20,23,24 and electron [25][26][27] dynamics. Although such techniques do not offer temporal resolution, they have been successfully used to provide an upper bound of dynamical processes, without the need for specialist equipment.…”