Molecule excitation

RRKM theory assumes a microcanonical ensemble of A vibrational/rotational states within the energy interval E E + dE, so that each of these states is populated statistically with an equal probability [4]. This assumption of a microcanonical distribution means that the unimolecular rate constant for A only depends on energy, and not on the maimer in which A is energized. If N(0) is the number of A molecules excited at / =... 

Definitive examples of intrinsic non-RRKM dynamics for molecules excited near their unimolecular tluesholds are rather limited. Calculations have shown that intrinsic non-RRKM dynamics becomes more pronounced at very high energies, where the RRKM lifetime becomes very short and dissociation begins to compete with IVR [119]. There is a need for establishing quantitative theories (i.e. not calculations) for identifying which molecules and energies lead to intrinsic non-RRKM dynamics. For example, at thenual... 

Another example of a teclmique for detecting absorption of laser radiation in gaseous samples is to use multiphoton ionization with mtense pulses of light. Once a molecule has been electronically excited, the excited state may absorb one or more additional photons until it is ionized. The electrons can be measured as a current generated across the cell, or can be counted individually by an electron multiplier this can be a very sensitive technique for detecting a small number of molecules excited. 

Plenary 9. J W Nibler et al, e-mail address niblerj chem.orst.edu (CARS and SRS). High resolution studies of high lymg vibration-rotational transitions in molecules excited in electrical discharges and low density monomers and clusters in free jet expansions. Ionization detected (REMPI) SRS or IDSRS. Detect Raman... 

The fluorescence signal is linearly proportional to the fraction/of molecules excited. The absorption rate and the stimulated emission rate 1 2 are proportional to the laser power. In the limit of low laser power,/is proportional to the laser power, while this is no longer true at high powers 1 2 <42 j). Care must thus be taken in a laser fluorescence experiment to be sure that one is operating in the linear regime, or that proper account of saturation effects is taken, since transitions with different strengdis reach saturation at different laser powers. 

Solvent-molecule excitation energy is transferred to the PPO molecules, often called the primary fluor or solute ... 

Excited states play important roles in chemistry. Recall from Chapter 7 that the properties of atoms can be studied by observing excited states. In fact, chemists and physicists use the characteristics of excited states extensively to probe the stmcture and reactivity of atoms, ions, and molecules. Excited states also have practical applications. 

Figure 13. Photodissociation spectrum of V (OCO), with assignments. Insets and their assignments show the photodissociation spectrum of molecules excited with one quanmm of OCO antisymmetric stretch, v" at 2390.9 cm . These intensities have been multiplied by a factor of 2. The shifts show that Vj (excited state) lies 24 cm below v ( (ground state), and that there is a small amount of vibrational cross-anharmonicity. The box shows a hot band at 15,591 cm that is shifted by 210 cm from the origin peak and is assigned to the V" -OCO stretch in the ground state.

In addition to the previously mentioned disadvantages, all of these methods have another drawback in the large molecule photofragment velocity measurements. For example, in the studies of UV photon photodissociation of polyatomic molecules, like alkene and aromatic molecules, molecules excited by the UV photons quickly become highly vibrationally excited in the ground electronic state through fast internal conversion, and dissociation occurs in the ground electronic state. 

Again, the calculation is identical to what we would make for fluorescence if the total number of molecules excited at time zero was Maii, but there were now two pathways of de-excitation. Notice that we can tell whether the t-door (the t-pathway) is open by measuring either the lifetime x( and comparing to xf, or measuring the intensity with the door open and again with the door closed,... 

S is the output gray value after the s.e. channel detector scaling (gs) of the sum of the fractions of donor fluorescence in the s.e. channel (FJ,) and of acceptor fluorescence in the s.e. channel (F) ). The donor fluorescence depends on Qd, the excitation efficiency at lfx (that is, Fe ), the number of donors (ND), and the population of donors that lose their energy by FRET (ENs-). The fluorescence of acceptors depends on QA, the amount of acceptor molecules (NA) excited with 2dx ( szsA) and on the amount of acceptor molecules excited by FRET (ENs, which is linear to Fefj). 

RET between like molecules. Excitation energy migration in assemblies of chromophores... 

Excited singlet oxygen has one electron promoted to a higher valence orbital making an unpaired electron and a highly reactive molecule. Excited singlet oxygen will... 

Detailed information about collision-induced, vibrational, or rotational excitation and deactivation has been collected from much work on molecular lasers, expecially the COj laser 1. If the intensity of a laser line is sufficiently high, its gain in an amplifying medium saturates and is then determined by the number of molecules excited per second into the upper laser level and by the depopulation rate of the lower level. Measuring the saturation behaviour under different pressures and discharge currents allows the excitation and deactivating processes to be studied Observation of the... 

Since thermal deactivation from high-lying electronically excited states occurs on the picosecond timescale [70, 71] for conjugated molecules, excitation energy... 

In Figure 10.12, the TE-CARS signal intensity largely surpasses the background because the number of molecules in the excited volume is enough to induce the large signal. It, however, depends on experimental conditions such as the number of molecules, excitation laser power, and optical density of samples. In other cases, the... 

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