Volume 123, Issue 14, 08 October 2005
Index of content:
123(2005); http://dx.doi.org/10.1063/1.2074457View Description Hide Description
Nonadiabatic wave-packet dynamics is factorized into purely adiabatic propagation and instantaneous localized nonadiabatic transition. A general formula is derived for the quantum-mechanical local nonadiabatic operator which is implemented within the framework of the -matrix method. The operator can be used for incorporating the nonadiabatic transition in semiclassical wave-packet dynamics.
123(2005); http://dx.doi.org/10.1063/1.2069865View Description Hide Description
We report a new form of microwave optical double-resonance spectroscopy called millimeter-wave-detected, millimeter-wave optical polarizationspectroscopy (mmOPS). In contrast to other forms of polarizationspectroscopy, in which the polarization rotation of optical beams is detected, the mmOPS technique is based on the polarization rotation of millimeter waves induced by the anisotropy from optical pumping out of the lower or upper levels of the millimeter wave transition. By monitoring ground-state rotational transitions with the millimeter waves, the mmOPS technique is capable of identifying weak or otherwise difficult-to-observe optical transitions in complex chemical environments, where multiple molecular species or vibrational states can lead to spectral congestion. Once a transition is identified, mmOPS can then be used to record pure rotational transitions in vibrationally and electronically excited states, with the resolution limited only by the radiative decay rate. Here, the sensitivity of this nearly-background-free technique is demonstrated by optically pumping the weak, nominally spin-forbidden CS and electronic transitions while probing the CS rotational transition with millimeter waves. The pure rotational transition of the CS state is then recorded by optically preparing the level of the state via the transition of the band.
Fragmentation of HCN in optically selected mass spectrometry: Nonthermal ion cooling in helium nanodroplets123(2005); http://dx.doi.org/10.1063/1.2046672View Description Hide Description
A technique that combines infrared laser spectroscopy and heliumnanodropletmass spectrometry, which we refer to as optically selected mass spectrometry, is used to study the efficiency of ion cooling in helium. Electron-impact ionization is used to form ions within the droplets, which go on to transfer their charge to the HCN dopant molecules. Depending upon the droplet size, the newly formed ion either fragments or is cooled by the helium before fragmentation can occur. Comparisons with gas-phase fragmentation data suggest that the cooling provided by the helium is highly nonthermal. An “explosive” model is proposed for the cooling process, given that the initially hot ion is embedded in such a cold solvent.