Two new methods for simultaneous measurement of velocity and internal state are reported, and results are presented for application of the techniques to the photodissociation of CH3I. The internal state of the probed fragment is chosen by tuning the resonant ionizing laser, while the fragment velocity is determined from the arrival time distribution of fragment ions at the detector of a time-of-flight (TOP) mass spectrometer. For the 266-nm dissociation of CH3I or CD3I, the amount of I*(1 2Pi/2) vs I(2P3/2) produced in coincidence with CH3(v2=i) or CD3(v2=y) has been determined for i = 0-2 and j = 0-3.The values are (i, I/I*) = (0, 0.08), (1, 0.37), (2, 1.1) and (j, I/I*) = (0, <0.05), (1, 0.09), (2, 0.19), (3, 0.68). These I/I* ratios were found to vary dramatically with probe wavelength, partly due to variations in ratio with methyl rotational level and partly due to different contributions from overlapping vibronic bands, in a further application, separate MPI wavelength scans were obtained simultaneously for CD3 produced in coincidence with I and I*. Observations on the I and I* fragments have allowed us to determine values for the anisotropy parameters (/3(I) = 1.7 ± 0.1, /3(I*) = 1.8 ± 0.1). Application of these techniques to the detection of clusters and to the discrimination between multiple pathways to the same fragment ion in multiphoton dissociation and ionization is discussed.to the Doppler method but requires neither sub-Doppler laser line (1)

The photodissociation dynamics of CH)I and CD31 have been examined by using multiphoton ionization to probe the CH), CD 3 , I( =5 2P3/2) and 1*( =15 2P 1/2 ) photoproducts. The parent compounds were cooled in a supersonic expansion, collimated into a molecular beam, and dissociated at 266 nm. For the CD31 dissociation, the ratio ofCD 3 (v = O)/(v = 2) was estimated to be about 1.1, with mUltiple determinations ranging from 0.47-2.1. The quantum number v here denotes the nascent excitation of the V 2 "umbrella" mode. Measurements of the CD 3 (v = 1) and (v = 3) vibronic bands indicated that the (v = 1) I (v = 3) ratio is greater than unity, with some measurements suggesting values as large as 10. A value for the CH 3 (v = O)/(v = 2) ratio from dissociation ofCH 3 1 could not be estimated, although it was clearly larger than that for CD 3 . The CH 3 (v = 0) and CD 3 (v = 0) products from this dissociation are fit by 120 ± 30 K and 105 ± 30 K rotational distributions, respectively. The dissociation mechanism produces alignment in the molecular frame such that there is a strong preference for K = 0 (rotation perpendicular to the top axis). Assuming that the relative velocity vector lies along the CH 3 C 3 axis, the velocity and rotation vectors tend to be perpendicular. It is likely that K = 0 molecular frame alignment is produced in photodissociation through both the I and 1* channels.ciation showed maximum popUlations of CH 3 in v = 2 and 4 4222

In the wake of the redefinition of the kilogram, the last unit of the International System of Units (SI) that is still based on a man-made artefact, discussions were launched on the necessity of redefining other units, amongst other the unit mole. Since 1971 the mole is defined as the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12. The symbol of the unit is 'mol'. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. The definition is based on the pre-existing choice to set the relative atomic mass of carbon 12 equal to 12 exactly. In the proposed new definition the mole is the amount of substance containing exactly 6.022 141 79 × 1023 atoms or molecules, ions, electrons, other particles, or specified groups of such particles, i.e. the Avogardo constant would have a fixed value without an uncertainty. This contribution critically examines the submitted arguments to justify the proposed redefinition of the unit mole by 2011 for their persuasive power to change a scientific and cultural good such as a unit of measurement. As shown, there are no convincing scientific arguments for a redefinition of the mole that stand a closer examination. The current definition is well understood, established in science and technology for almost 50 years and is still up to date.

The evaluation results of the metrological performance of a dilution and a permeation standard for generating SI-traceable calibration gas mixtures of NO, SO2 and NO2 for ambient air measurements are presented. The composition of the in situ produced reference gas mixtures is calculated from the instantaneous values of the input quantities of the generating standards. In a measurement comparison, the calibration and measurement capabilities of five laboratories were evaluated for the three analytes at limiting amount of substance fractions in ambient air between 20 and 150 nmol mol−1. For the upper generated reference values the target relative uncertainties of  ⩽2% (for NO and SO2) and  ⩽3% (for NO2) for evaluating the laboratory results were fulfilled in 12 out of 13 cases. For the analytical results seven out of nine laboratories met the criteria for the upper values for NO and NO2, for SO2 it was one out of four. From the negative degrees of equivalence of all NO2 comparison results it was supposed that the permeation rate of NO2 through the FEP polymer membrane of the permeator was different in air and N2. Subsequent precision permeation measurements with various carrier gases revealed that the permeation rate of NO2 was  ≈0.8% lower in synthetic air compared to N2. With the corrected NO2 reference values for air the degrees of equivalence of the laboratory results were improved and closer to be symmetrically distributed.

Correlations between either scalar or vector quantities measured in the study of photodissociation dynamics can serve to provide a very detailed picture of the dissociative event. This article discusses the use of Doppler profile and time-of-flight spectroscopy to learn about the correlation between the separate internal energies of two recoiling fragments, to study the way in which the internal energy distribution of a fragment varies with its recoil direction and to determine the angle between a photofragment's recoil velocity direction and its rotation vector. Two new techniques are introduced. High-voltage switching of the potential applied to a time-of-flight mass spectrometer is used to map the velocity distribution of photofragments onto their arrival time distribution. Probing of photofragments by polarized light with sub-Doppler resolution is used to determine the degree of angular correlation between their rotation vector and their recoil velocity vector.