Transition rovibronic

Vibrational transitions accompanying an electronic transition are referred to as vibronic transitions. These vibronic transitions, with their accompanying rotational or, strictly, rovibronic transitions, give rise to bands in the spectrum, and the set of bands associated with a single electronic transition is called an electronic band system. This terminology is usually adhered to in high-resolution electronic spectroscopy but, in low-resolution work, particularly in the liquid phase, vibrational structure may not be resolved and the whole band system is often referred to as an electronic band. 

Even in a molecule the size of benzene the resolution achieved in this way is sufficient to investigate the dynamic behavior of individual rotational states. For this it is necessary to eliminate the Doppler broadening of the rovibronic transitions. Two methods have been applied (i) the elimination of Doppler broadening in a Doppler-free two-photon-transition and (ii) the reduction of Doppler broadening in a molecular beam. Measurements of the dynamic behavior have been performed in the frequency [3] and time domain [4]. We will briefly summarize the results from high-resolution measurements and discuss the conclusions on the intramolecular decay mechanism. Then it will be discussed how the intramolecular dynamics is influenced by the attachment of an Ar or Kr atom to the benzene molecule, leading to a weakly bound van der Waals complex. 

BaO was produced by allowing barium vapour in an argon carrier to interact with traces of oxygen. Microwave power was introduced by means of a simple horn situated close to the optical interaction zone. By tuning the dye laser frequency to coincide exclusively with a succession of rovibronic transitions, it was possible to observe and measure four rotational transitions in the X 1 + ground state, involving both v = 0 and v = 1, and thirteen rotational transitions in the A 1 X excited electronic state. From these measurements accurate values of the rotational constants were obtained, particularly for the excited state. 

In a similar way, 1+1)-REMPI has been used to identify the Si2 molecules desorbing from the Si wire surface (m/e = 56) by three rotational-vibrational-electronic (rovibronic) transition lines of the (v = 5) <— (v" == 0) vibrational transition in the H X Zg" electronic band. These signals are, however,... 

Although most experiments have so far been performed with dye lasers, the color-center lasers or the newly developed vibronic solid-state lasers such as the Tiisapphire laser, with broad spectral-gain profiles (Vol. 1, Sect. 5.7.3) are equally well suited for intracavity spectroscopy in the near infrared. An example is the spectroscopy of rovibronic transitions between higher electronic states of the H3 molecule with a color-center laser [24]. The combination of Fourier spectroscopy with ICLAS allows improved spectral resolution, while the sensitivity can also be enhanced [25, 34, 35]. 

The application of OODR in molecular beams to the analysis of complex perturbed spectra is illustrated by Fig. 5.21, which shows a section of the visible NO2 spectrum around X = 488 nm. In spite of the small residual Doppler width of 15 MHz, not all lines are fully resolved and the analysis of the spectrum turns out to be very difficult, because the upper state is heavily perturbed. If in the OODR experiment the pump laser Li is kept on line 1, one obtains the two OODR signals as shown in the upper left part of Fig. 5.21, which proves that lines 1 and 4 in the lower spectrum share a common lower level. The right part of Fig. 5.21 also shows that the lines 2 and 5 start from a common lower level as well as the lines 3 and 6. The whole lower spectrum consists of two rovibronic transitions 7", K" = (10,5) (/, K ) = (11,5) (each with three hfs components), which end in two closely spaced rotational levels with equal quantum numbers (/, K ) that belong to two different vibronic states coupled by a mutual interaction [547]. 

Collision-Induced Rovibronic Transitions in Excited States... 

In fact, the / value usually does change during a rovibrational or rovibronic transition, even though the rotational state has relatively little impact on the overall transition energy. In electric-dipole transitions, the photon transfers one unit of angular momentum to the molecule, and this must be absorbed by the... 

Extending these principles to nonlinear molecules, and to rovibronic transitions, the selection rules for / can be written simply as... 

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