Inelastic scattering is a fundamental collisional process that plays an important role in many areas of chemistry, and its detailed study can provide valuable insight into more complex chemical systems. Here, we report the measurement of differential cross-sections for the rotationally inelastic scattering of NO(X2Π1/2, v=0, j=0.5, f) by Ar at a collision energy of 530 cm(-1) in unprecedented detail, with full Λ-doublet (hence total NO parity) resolution in both the initial and final rotational quantum states. The observed differential cross-sections depend sensitively on the change in total NO parity on collision. Differential cross-sections for total parity-conserving and changing collisions have distinct, novel quantum-mechanical interference structures, reflecting different sensitivities to specific homonuclear and heteronuclear terms in the interaction potential. The experimental data agree remarkably well with rigorous quantum-mechanical scattering calculations, and reveal the role played by total parity in acting as a potential energy landscape filter.

The first measurements of differential inelastic collision cross sections of fully state-selected NO ͑j =1/2, ⍀ =1/2, ⑀ =−1͒ with He are presented. Full state selection is achieved by a 2 m long hexapole, which allows for a systematic study of the effect of parity conservation and breaking on the differential cross section. The collisionally excited NO molecules are detected using a resonant ͑1+1Ј͒ REMPI ionization scheme in combination with the velocity-mapped, ion-imaging technique. The current experimental configuration minimizes the contribution of noncolliding NO molecules in other rotational states j , ⍀ , ⑀ -that contaminates images-and allows for study of the collision process at an unprecedented level of detail. A simple method to correct ion images for collision-induced alignment is presented as well and its performance is demonstrated. The present results show a significant difference between differential cross sections for scattering into the upper and lower component of the ⌳-doublet of NO. This result cannot be due to the energy splitting between these components.

Fully Λ-doublet resolved state-to-state differential cross-sections (DCSs) for the collisions of the open-shell NO(X, (2)Π(1/2), ν = 0, j = 0.5) molecule with Ar at a collision energy of 530 cm(-1) are presented. Initial state selection of NO(X, (2)Π(1/2), j = 0.5, f) was performed using a hexapole so that the (low field seeking) parity of ε = -1, corresponding to the f component of the Λ-doublet, could be selected uniquely. Although the Λ-doublet levels lie very close in energy to one another and differ only in their relative parities, they exhibit strikingly different DCSs. Both spin-orbit conserving and spin-orbit changing collisions have been studied, and the previously unobserved structures in the fully quantum state-to-state resolved DCSs are shown to depend sensitively on the change in parity of the wavefunction of the NO molecule on collision. In all cases, the experimental data are shown to be in excellent agreement with rigorous quantum mechanical scattering calculations.

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A novel method for applying cavity ring-down spectroscopy in the liquid phase, compatible with LC analyses, is presented. The core of the setup is a home-built cavity ring-down flow cell (cell volume 12 µL) that is constructed using a silicon rubber spacer, which is clamped leak-tight between two high-reflectivity mirrors. The mirrors are in direct contact with the liquid flow, which provides for a small path length and short ring-down times. Inside the cavity there are no windows, reflection losses, or Brewster angles to be considered. Due to the small size of the presented cavity geometry, the setup can be implemented in conventional-size LC apparatuses. With a flow injection setup, a detection limit of 2.5 nM was obtained for Crystal Violet in ethanol, and the linear dynamic range of the system is at least 2 orders of magnitude. The method has the potential to become a powerful alternative for commercial LC UV/visible absorbance detectors.In liquid chromatography (LC), direct optical absorption is the generic and commonly used method to detect absorbing analytes and their concentration in eluting compounds. Almost any analyte absorbs light in the visible or ultraviolet range, and standard absorption detection shares the advantages of simplicity and versatility. Since direct absorption techniques are based on monitoring attenuation of light intensity, they are fundamentally limited by the intensity fluctuations of the light sources employed, where currently ∆I/I values of 5 × 10 -5 are reached. 1 An option for improving the limit of detection (LOD) in LC lies in the increase of the optical path length without altering the detector cell volume, and therefore, Z-shaped cells of typically 8-mm optical path length and 1-mm diameter are commonly used. With the use of liquid core waveguide flow cells, optical path lengths as long as 30-50 cm can be obtained, 2,3 but the number of applications is still limited. Considering the broad applicability of absorption detection in LC, it is highly relevant to improve sensitivity and detection limits, but at the same time, the chromatographic restrictions of LC should be complied with. In view of chromatographic band-broadening effects, even in conventional-size LC the detector cell volume should be limited to typically 20 µL, while for micro-and especially nano-LC, the constraints on detection volumes are obviously much more serious.The invention of the cavity ring-down (CRD) detection technique 4 has introduced an elegant manner for improving sensitivity in direct absorption. CRD is based on the injection of a short laser pulse into an optical resonator with high-reflectivity mirrors, followed by the detection of the light leaking away through a mirror. Since its principle is based on measuring the rate of decay of an optical cavity, CRD in effect circumvents the common limitations of absorption measurements: the decay time is independent of the intensity of the light pulse exciting the optical resonator, and hence, pulsed laser sources with pulse-to-pulse intensity fluctua...