Cation-π Complexes of Silver Studied with Photodissociation and Velocity-Map Imaging.

Ag+(aromatic) ion-molecule complexes of benzene, toluene, or furan are generated in the gas phase by laser vaporization in a supersonic expansion. These ions are mass selected in a time-of-flight spectrometer and studied with ultraviolet laser photodissociation and photofragment imaging. UV laser excitation results in dissociative charge transfer (DCT) for these ions, producing neutral silver atom and the respective aromatic cation as the photofragments. Velocity-map imaging and slice imaging techniques are employed to investigate the kinetic energy release in these photodissociation processes. In each case, DCT produces significant kinetic energy, and evidence is also found for excitation of the internal rovibrational degrees of freedom for the molecular cations. Analysis of the kinetic energy release together with the known ionization energies of silver and the molecular ligands provides new information on the cation-π bond energies.

Infrared spectroscopy of H+(CO)2 in the gas phase and in para-hydrogen matrices.

The H+(CO)2 and D+(CO)2 molecular ions were investigated by infrared spectroscopy in the gas phase and in para-hydrogen matrices. In the gas phase, ions were generated in a supersonic molecular beam by a pulsed electrical discharge. After extraction into a time-of-flight mass spectrometer, the ions were mass selected and probed by infrared laser photodissociation spectroscopy in the 700 cm-1-3500 cm-1 region. Spectra were measured using either argon or neon tagging, as well as tagging with an excess CO molecule. In solid para-hydrogen, ions were generated by electron bombardment of a mixture of CO and hydrogen, and absorption spectra were recorded in the 400 cm-1-4000 cm-1 region with a Fourier-transform infrared spectrometer. A comparison of the measured spectra with the predictions of anharmonic theory at the CCSD(T)/ANO1 level suggests that the predominant isomers formed by either argon tagging or para-hydrogen isolation are higher lying (+7.8 kcal mol-1), less symmetric isomers, and not the global minimum proton-bound dimer. Changing the formation environment or tagging strategy produces other non-centrosymmetric structures, but there is no spectroscopic evidence for the centrosymmetric proton-bound dimer. The formation of higher energy isomers may be caused by a kinetic effect, such as the binding of X (=Ar, Ne, or H2) to H+(CO) prior to the formation of X H+(CO)2. Regardless, there is a strong tendency to produce non-centrosymmetric structures in which HCO+ remains an intact core ion.

From the tunneling dimer to the onset of microsolvation: Infrared spectroscopy of allyl radical water aggregates in helium nanodroplets.

The infrared spectrum of allyl:water clusters embedded in helium nanodroplets was recorded. Allyl radicals were produced by flash vacuum pyrolysis and trapped in helium droplets. Deuterated water was added to the doped droplets, and the infrared spectrum of the radical water aggregates was recorded in the frequency range 2570-2820 cm-1. Several absorption bands are observed and assigned to 1:1 and 1:2 allyl:D2O clusters, based on pressure dependent measurements and accompanying quantum chemical calculations. The analysis of the 1:1 cluster spectrum revealed a tunneling splitting as well as a combination band. For the 1:2 cluster, we observe a water dimer-like motif that is bound by one π-hydrogen bond to the allyl radical.

Infrared spectroscopy of the ν2 band of the water monomer and small water clusters (H2O)n=2,3,4 in helium droplets.

We have recorded infrared spectra in the frequency range of the ν2 band of water monomer and water clusters in superfluid helium droplets. In order to be able to map the chemically important fingerprint range, we have used an IR quantum cascade laser as a radiation source. We were able to observe three ro-vibrational transitions of the water monomer between 1590 and 1670 cm(-1). The lines were assigned to the 110 ← 101, 111 ← 000 and 212 ← 101 transitions of the ν2 vibration of H2O. Based upon the linewidths, we could deduce relaxation times of 1.9 to 4.2 ps for the monomer. Additional absorption bands could be assigned to ν2 vibrational bands of water clusters (H2O)n with n = 2, 3, 4. These experimental results are compared to theoretical calculations by Wang and Bowman which are reported in an accompanying paper [ref. 1, Y. Wang and J. M. Bowman, Phys. Chem. Chem. Phys., 2016, DOI: ]. We find a very good agreement of our results with both calculations and with previous results from gas phase cavity ringdown experiments.

Helium droplet infrared spectroscopy of glycine and glycine-water aggregates.

Infrared absorption spectra of glycine and glycine-water aggregates embedded in superfluid helium nanodroplets were recorded in the frequency range 1000-1450 cm-1. For glycine monomer, absorption bands were observed at 1106 cm-1, 1134 cm-1, and 1389 cm-1. These bands were assigned to the C-OH stretch mode of the glycine conformers I, III and II, respectively. For glycine-water aggregates, we observed two bands at 1209 cm-1 and 1410 cm-1 which we assign to distinct conformers of glycine-H2O. In all cases, the water is found to preferentially bind to the carboxyl group of the glycine.

Infrared spectroscopy of the helium solvated cyclopentadienyl radical in the CH stretch region.

Cyclopentadienyl radicals were produced by vacuum flash pyrolysis and trapped in superfluid helium nanodroplets. The infrared spectrum of the embedded radicals was recorded in the range 3020-3120 cm(-1). Three bands observed at 3056.3, 3086.9, and 3117.3 cm(-1) were assigned to the transitions from the ground state to the three levels of the quadratically Jahn-Teller distorted (i.e., second order Jahn-Teller active) CH stretch vibration with E1' symmetry. Accompanying ab initio calculations showed a vibrationally averaged symmetric equilibrium structure in agreement with the observed vibronic transitions. Our results confirm a symmetric configuration of the cyclopentadienyl (cp) radical that is dynamically Jahn-Teller distorted. Density functional theory calculations and infrared data further suggest that barrier-less reactions of two cp radicals occur within the droplets.

Understanding the microsolvation of radicals: Infrared spectroscopy of benzyl radical water clusters.

The IR spectrum of benzyl radical:water clusters was recorded. Benzyl radicals were produced by vacuum flash pyrolysis and trapped in superfluid helium nanodroplets. The infrared spectrum of benzyl radical water aggregates in the range 2585-2820 cm-1 was recorded by subsequent addition of deuterated water. A total of seven peaks are observed at 2766, 2750, 2656, 2638, 2633, 2598, and 2593 cm-1. Based on pressure dependent measurements and comparison to accompanying ab initio calculations, five of these bands are assigned to distinct O-D stretch vibrations of benzyl:water clusters with one and two water molecules. In line with previous experiments on benzene:water clusters, we observe the formation of a water dimer-like motif that is attached to one face of the benzyl radical.

Complexation of allyl radicals and hydrochloric acid in helium nanodroplets.

Infrared spectra of the allyl radical-HCl complex in superfluid helium nanodroplets have been recorded in the IR frequency range of 2750-3120 cm(-1). Six fundamental bands were observed, five of which have been assigned to the C-H stretch vibrations of the allyl radical. No additional CH bands were observed upon the binding of HCl. The band at 2800.3 cm(-1) can unambiguously be assigned to the bound HCl stretch, which is red-shifted by 106 cm(-1) compared to that of the free HCl. Stark spectra and pickup curves were recorded and support our assignment. In accompanying ab initio calculations, we found four equivalent minima and computed a two-dimensional potential energy surface for the HCl positioning on the allyl radical plane at the CCSD(T)/TZVPP level. Based on our findings, we conclude that the ground-state structure of the complex shows two energetically equivalent T-shaped minimum structures. Because of small barriers between the two minima, a delocalization of the HCl is anticipated.

Reassignment of ν2,3 IR band of the allyl radical in liquid helium nanodroplets.

We have recorded the IR-spectrum of the deuterated allyl radical in the frequency range of the CH stretch vibrations in liquid helium nanodroplets. Comparison to the allyl radical spectrum enabled us to make an unambiguous assignment. Based on these new experimental measurements, a reassignment of the ν2,3 IR bands was deemed necessary.

IR-spectroscopic study of the allyl + NO reaction in helium nanodroplets.

The IR-spectrum of the allyl-NO adduct (CH2-CH-CH2-NO) in helium nanodroplets has been recorded in the frequency region 2850-3120 cm(-1). CH2-CH-CH2-NO has been investigated as a prototype of the product of radical-radical reactions at 0.37 K. The product of the reaction, 3-nitroso-1-propene, was formed via the reaction of allyl and NO within the helium droplets. For an assignment we have predicted the conformers of the CH2-CH-CH2-NO using density functional theory (DFT) with a BLYP functional and a TZVPP basis set. By comparison with the experimental spectrum we can show that all three conformers are stabilized in superfluid helium nanodroplets.

Computer-aided planning with exact implementation into surgical technique in TKA is as accurate as intraoperative navigation.

BACKGROUND: Exact positioning of implants and accuracy of alignment are important parameters to provide an long survivorship of endoprostheses after total knee arthroplasty. It was suggested that an alignment within 3∘ from centerline provides the best long-term survivorship of TKA. Therefore, computer-assisted navigation became more important in TKAs. Another tool to improve the accuracy in TKA is the preoperative planning software. OBJECTIVE: Main goal was to determine if advantages of an intraoperative navigation system during TKA can be reached by an exact implementation of a preoperative computer-aided planning. METHODS: Based on all patients (n= 100) underwent primarily TKA in 2015 and 2016 two groups were declared: (1) conventionally operated TKA without navigation system and (2) operation with an optical navigation system. Data on age, sex, date, operative time, severe complications and preoperative vs. postoperative alignment were collected retrospectively. RESULTS: The two groups do not differ in postoperative alignment and frequency of outliers. Furthermore, there was no difference referring to complications and the length of stay in hospital, but operative time was prolonged in the navigation-assisted group. CONCLUSIONS: It can be stated that conventional surgical techniques in TKA are as accurate as navigated ones if an exact preoperative computer aided planning is implemented during surgery.