Conical intersection topography plays an essential role in excited-state photochemistry. Here, topography is modified systematically to quantify its effects on photochemical reaction rates, reactant recovery, and photoproduct yield.

We report a measurement of the nuclear polarization of laser-cooled, optically pumped 37 K atoms which will allow us to precisely measure angular correlation parameters in the b + -decay of the same atoms. These results will be used to test the V−A framework of the weak interaction at high precision. At the TRIUMF neutral atom trap (TRINAT), a magneto-optical trap confines and cools neutral 37 K atoms and optical pumping spin-polarizes them. We monitor the nuclear polarization of the same atoms that are decaying in situ by photoionizing a small fraction of the partially polarized atoms and then use the standard optical Bloch equations to model their population distribution. We obtain an average nuclear polarization of¯=  P 0.9913 0.0009, which is significantly more precise than previous measurements with this technique. Since our current measurement of the β-asymmetry has 0.2% statistical uncertainty, the polarization measurement reported here will not limit its overall uncertainty. This result also demonstrates the capability to measure the polarization to <0.1%, allowing for a measurement of angular correlation parameters to this level of precision, which would be competitive in searches for new physics.

Vibronic coupling between electronic and vibrational states in molecules plays a critical role in most photo-induced phenomena. Many key details about a molecule’s vibronic coupling are hidden in linear spectroscopic measurements, and therefore nonlinear optical spectroscopy methods such as two-dimensional electronic spectroscopy (2D ES) have become more broadly adopted. A single vibrational mode of a molecule leads to a Franck–Condon progression of peaks in a 2D spectrum. Each peak oscillates as a function of the waiting time, and Fourier transformation can produce a spectral slice known as a ‘beating map’ at the oscillation frequency. The single vibrational mode produces a characteristic peak structure in the beating map. Studies of single modes have limited utility, however, because most molecules have numerous vibrational modes that couple to the electronic transition. Interactions or interference among the modes may lead to complicated peak patterns in each beating map. Here, we use lineshape-function theory to simulate 2D ES arising from a system having multiple vibrational modes. The simulations reveal that the peaks in each beating map are affected by all of the vibrational modes and therefore do not isolate a single mode, which was anticipated.

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