Internal quantum states, measurements

Optical metiiods, in both bulb and beam expermrents, have been employed to detemiine tlie relative populations of individual internal quantum states of products of chemical reactions. Most connnonly, such methods employ a transition to an excited electronic, rather than vibrational, level of tlie molecule. Molecular electronic transitions occur in the visible and ultraviolet, and detection of emission in these spectral regions can be accomplished much more sensitively than in the infrared, where vibrational transitions occur. In addition to their use in the study of collisional reaction dynamics, laser spectroscopic methods have been widely applied for the measurement of temperature and species concentrations in many different kinds of reaction media, including combustion media [31] and atmospheric chemistry [32]. 

Schematic energy level diagrams for the most widely used probe methods are shown in Fig. 1. In each case, light of a characteristic frequency is scattered, emitted, and/or absorbed by the molecule, so that a measurement of that frequency serves to identify the molecule probed. The intensity of scattered or emitted radiation can be related to the concentration of the molecule responsible. From measurements on different internal quantum states (vibrational and/or rotational) of the system, a population distribution can be obtained. If that degree of freedom is in thermal equilibrium within the flame, a temperature can be deduced if not, the population distribution itself is then of direct interest.

Margulis GY, Hardin BE, Ding IK, Hoke ET, McGehee MD (2013) Parasitic absorption and internal quantum efficiency measurements of solid-state dye sensitized solar cells. Adv Energ Mater 3(7) 959-966... 

Tunable laser spectroscopic techniques such as laser-induced fluorescence (LIF) or resonantly enhanced multi-photon ionization (REMPI) are well-established mature fields in gas-phase spectroscopy and dynamics, and their application to gas-surface dynamics parallels their use elsewhere. The advantage of these techniques is that they can provide exceedingly sensitive detection, perhaps more so than mass spectrometers. In addition, they are detectors of individual quantum states and hence can measure nascent internal state population distributions produced via the gas-surface dynamics. The disadvantage of these techniques is that they are not completely general. Only some interesting molecules have spectroscopy amenable to be detected sensitively in this fashion, e.g., H2, N2, NO, CO, etc. Other interesting molecules, e.g. 02, CH4, etc., do not have suitable spectroscopy. However, when applicable, the laser spectroscopic techniques are very powerful. 

A typical application is the use of the (2 + 1) REMPI scheme for measuring the (v,./) distribution of H2 produced in associative desorption from a surface. When the laser is tuned to a spectroscopic transition between individual quantum states in the X -> E electronic band, resonant two-photon absorption populates the E state and this is subsequently ionized by absorption of another photon. The ion current is proportional to the number in the specific (v,./) quantum state in the ground electronic state that is involved in the spectroscopic transition. Tuning the laser to another spectroscopic feature probes another (v, J) state. Therefore, recording the ion current as the laser is scanned over the electronic band maps out the population distribution of H2(v, J) produced in the associative desorption. Ef of the (v, J) state can also often be simultaneously measured using field - free ion TOF or laser pump - probe TOF detection techniques. The (2 +1) REMPI scheme for detecting H2 is almost independent of the rotational alignment and orientation f(M) of molecules so that only relative populations of the internal states... 

In competition to electron transfer processes is internal conversion (IC), in which deactivations of excited states occur via a nonradiative transition to the electronic ground state. Visualizing IC rates is practically impossible because of the lack of a direct probe mechanism for nonradiative transitions. A notable approach to overcome this lack of detectability implies fluorescence quantum yield measurements, which is, however, only indirect. 

Any quantum system can be associated to an I-frame thereby, internal and "external" (I-frame) quantum states can be determined or at least observed as done in astronomy. Probing (measuring) a quantum system breaks Hilbert space-time evolution thereby preparing a new quantum state. This latter can be used to detect the result due to probing. See Ref. [29] for an illustration. Gravitation is a prototype of classical effects. From neutron interference spectroscopy gravitation effects on quantum states are well documented. 

If one puts two electrons per quantum state ("spin-up and spin-down"), then the minimum resistance becomes 2R0 = 25.812986 kQ. The internal resistance of a molecule has not yet been measured. Recently, it was shown that a degenerate quasi-one-dimensional electron gas in a GaAs GaAh YAsY system, when interrogated in a four-probe geometry, has zero resistance drop between probes 2 and 3, in contrast to the expected R0 between probes 1 and 4 the transport is ballistic [13]. 

The most detailed information on the collision process can be obtained from laser spectroscopy of crossed-beam experiments, where the initial quantum states of the collision partners before the collision are marked, and the scattering angle as well as the internal energy of the reactants is measured. In such an ideal scattering experiment aU relevant parameters are known (Sect. 8.5). 

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