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The feasibility of complete photoionization experiments, in which the full set of photoionization matrix elements is determined, using multiphoton ionization schemes with polarization-shaped pulses has recently been demonstrated [P. Hockett et al., Phys. Rev. Lett. 112, 223001 (2014)]. Here we extend our previous work to discuss further details of the numerics and analysis methodology utilized and compare the results directly to new tomographic photoelectron measurements, which provide a more sensitive test of the validity of the results. In so doing we discuss in detail the physics of the photoionization process and suggest various avenues and prospects for this coherent multiplexing methodology. [ABSTRACT FROM AUTHOR]

Weak-field coherent control of a two-photon transition in colloidal semiconductor nanocrystals (NCs) by tailored femtosecond laser pulses is demonstrated at room temperature. Ensembles of cadmium sulfide (CdS) and cadmium selenide (CdSe) NCs forming a colloidal suspension were irradiated by ultrashort infrared laser pulses being phase-modulated in frequency domain. The luminescence generated by electron–hole recombination after two-photon excitation (TPE) of the shaped pulses serves as a measure for NC excitation. In the experiment, we applied polynomial spectral phase functions of second- (GDD) and third-order (TOD), as well as phase jumps (θ-step), and studied the effect of the various shaped laser pulses on the excitation of both types of NCs. In view of potential applications in multilabel two-photon microscopy, both types of NCs are uniformely mixed in a single sample. We find that distinct pulse shapes enable selectivity among the excitation of both NC types in this mixture. Numerical simulations based on calculating the spectral overlap of the second order nonlinear optical spectrum and the TPE spectrum of the NCs are in good agreement with the measurement results. Analytic expressions derived for the second order power spectral density (PSD) because of combined GDD-TOD modulation and the θ-step rationalize this finding and show that GDD-TOD modulation provides a spectroscopic tool to investigate the TPE spectrum.

The rate constants for the reactions of the hydroxyl radical, HO and DO, with 2-vinylfuran (k₁ and k₂) were measured at 295 ± 2 K using the method of pulsed laser photolytic generation of HO or DO, combined with pulsed laser induced fluorescence detection. For DO, mono-exponential decay profiles were observed, enabling a simple analysis to extract a value of k₂ = (8.8 ± 0.9) × 10−11 cm3 molecule−1 s−1. In contrast, the decay of HO was complex, due to its regeneration in secondary reactions, and was analysed using a multi-exponential expression that enabled a rate constant of k₂ = (9.0 ± 1.0) × 10−11 cm3 molecule−1 s−1 to be extracted. The different behaviour of HO and DO provides clues to the reaction mechanism, which involves ring opening and a rearrangement/HO-elimination step. As part of this work the UV-absorption spectrum of 2-vinylfuran is also reported.

The position dependent 15N fractionation of nitrous oxide (N2O), which cannot be obtained from mass spectrometric analysis on molecular N2O itself, can be determined with high precision using isotope ratio mass spectrometry on the NO+ fragment that is formed on electron impact in the source of an isotope ratio mass spectrometer. Laboratory UV photolysis experiments show that strong position dependent 15N fractionations occur in the photolysis of N2O in the stratosphere, its major atmospheric sink. Measurements on the isotopic composition of stratospheric N2O indeed confirm the presence of strong isotope enrichments, in particular the difference in the fractionation constants for 15N14NO and 14N15NO. The absolute magnitudes of the fractionation constants found in the stratosphere are much smaller, however, than those found in the lab experiments, demonstrating the importance of dynamical and also additional chemical processes like the reaction of N2O with O(1D).

The title reactions were investigated using pulsed laser photolysis combined with pulsed laser induced fluorescence detection of CH3O to determine the rate coefficients for CH3 + NO2 → products (3) and CH3O + NO2 → products (5) as a function of temperature and pressure, and to estimate the yield of CH3 (and thus the yield of CH3C(O)OH) from the reaction of OH with CH3C(O)CH3 (2) at two different temperatures. Reaction 3 has both bimolecular and termolecular components:  a simplified falloff parametrization with Fcent = 0.6 gives %@mt;sys@%%@ital@%k%@rsf@%%@sx@%3b%@be@%0%@sxx@%%@mx@% = (3.2 ± 1.3) × 10^-28(T/297)^-0.3 cm⁶ s^-1 and %@mt;sys@%%@ital@%k%@rsf@%%@sx@%3b%@be@%∞%@sxx@%%@mx@% = (4.3 ± 0.4) × 10^-11(T/297)^-1.2 cm³ s^-1 with CH3NO2 the likely product. The rate constant for the bimolecular reaction pathway to form CH3O + NO (3a) was found to be 1.9 × 10^-11 cm^-3 s^-1. The low- and high-pressure limiting rate coefficients for reaction between CH3O and NO2 to form CH3ONO2 (5b) were derived as %@mt;sys@%%@ital@%k%@rsf@%%@sx@%5b%@be@%0%@sxx@%%@mx@% = (5.3 ± 0.3) × 10^-29(T/297)^-4.4 cm⁶ s^-1 and %@mt;sys@%%@ital@%k%@rsf@%%@sx@%5b%@be@%∞%@sxx@%%@mx@% = (1.9 ± 0.05) × 10^-11(T/297)^-1.9 cm³ s^-1, respectively. Although the final result is associated with some experimental uncertainty, we find that CH3 is formed in the reaction between OH and CH3C(O)CH3 at ≈50% yield at room temperature and 30% at 233 K.

The kinetics of the title reaction were investigated between 202 and 395 K and at 20, 50, and 100 Torr of Ar or N2 bath gas using pulsed laser photolysis (PLP) generation of OH combined with both resonance fluorescence (RF) and laser-induced fluorescence (LIF) detection. OH was generated either by the sequential 439 nm, two-photon dissociation of NO2 in the presence of H2, or by HONO photolysis at 351 nm. The accuracy of the rate constants obtained was enhanced by optical absorption measurements of acetone concentrations both before and after the photolysis reactor. The temperature dependence is not described by a simple Arrhenius expression but by k1 (202−395 K) = 8.8 × 10^-12 exp(−1320/T) + 1.7 × 10^-14 exp(423/T) cm³ s^-1, indicating that a simple H atom abstraction may not be the only reaction mechanism. The estimated total error (95% confidence) associated with the rate coefficient derived from this expression is estimated as 5% and is independent of temperature. The curvature in the Arrhenius plot results in a significantly larger rate coefficient at low temperatures than obtained by extrapolation of the previous measurement and implies greater significance for the reaction with OH as a sink for acetone in the upper troposphere than presently assumed.

Photoelectron interferograms, manifested in photoelectron angular distributions (PADs), are high-information, coherent observables. In order to obtain the maximum information from angle-resolved photoionization experiments it is desirable to record the full, three-dimensional (3D), photoelectron momentum distribution. Here we apply tomographic reconstruction techniques to obtain such 3D distributions from multiphoton ionization of potassium atoms, and fully analyze the energy and angular content of the 3D data. The PADs obtained as a function of energy indicate good agreement with previous 2D data and detailed analysis [Hockett et al., Phys. Rev. Lett. 112, 223001 (2014)] concerning the main spectral features, but also indicate unexpected symmetry breaking in certain regions of momentum space, thus revealing additional continuum interferences which cannot otherwise be observed. These observations reflect the presence of additional ionization pathways and, most generally, illustrate the power of maximum-information measurements of coherent observables for quantum metrology of complex systems. [ABSTRACT FROM AUTHOR]