Depletion spectra

Fig. 3. (A) Depletion spectra probed at 2 ps and (B) depletion kinetics trace for Ml 1. In graph (A), the ESA spectra with the depletion pulse present (dashed line) and without the depletion pulse (continuous line) are shown. Their difference is represented by the gray area. In graph (B), the curve represents a fit with single exponential rise and decay times, probed at 570 nm. The depletion was at 1000 nm for both graphs.

Parent ion depletion spectra for BrHI -Ar and BrDI"-Ar are shown in Fig. 3.4. Compared to the IR spectra of the symmetric bihalides, these spectra are considerably more complex and their assignment, based on previous calculations [41], was problematic. The two most intense peaks in both spectra correspond closely to the peaks seen in the previous matrix works. Their frequencies exhibit red-shifts when going from the gas phase to the matrix from 12 to 64 cm"i. All these peaks were assigned to the type I structure in the matrix. No peaks assigned to type II anions are observed in the gas phase, but additional peaks are observed in the gas phase spectra. In order to reach a satisfactory assignment of all the peaks observed... 

The agreement between calculated and experimentally measured optically allowed transitions for the most stable structures is very satisfactory. This means that the depletion spectra of neutral clusters, even if recorded at relatively high temperature [13], still reflect the structural properties this aspect will be addressed separately in Section 2.4, when discussing the distinct temperature behavior of different isomers close in energy. It will be shown that the isomerization processes take place for different cluster sizes at distinct temperatures. 

The first depletion spectra obtained for neutral sodium clusters N = 2-40 were characterized by structureless broad features containing one or two bands. The results were interpreted in terms of collective resonances of valence electrons (plasmons) for all clusters larger than tetramers [2, 52-55]. The analogies between findings for metallic clusters and observations of giant dipole resonances in nuclei have attracted a large attention. Therefore the methods employed in nuclear physics, such as different versions of RPA in connection with the jellium model, have also been applied for studying the optical properties of small clusters. Another aspect was the onset of conductivity in metal-insulator transitions. 

Fig. 18 IR-UV depletion spectra of doubly protonated GS (a) conformer A (b) conformer B (c) conformer C measured by fixing UV laser wavenumber on their respective peaks A1-A4, B and C (the largest peak only) in Fig. 18...

Figure 18 shows IR-UV depletion spectra of [GS + 2H] measured by fixing the UV laser wavenumber to transitions assigned to conformers A, B, and C in the spectrum of Fig. 17a. Each IR spectrum reflects the specific vibrational frequencies associated with the different conformers giving rise to the probed UV transitions. Several IR bands in the spectrum of conformer A appear to be doubly degenerate. For example, the five peaks lying between 1,600 and 1,700 cm belong to the ten bands that have primarily C=0 stretch character. This double degeneracy implies that pairs of oscillators are situated in equivalent positions in the molecule, and since GS is cyclic, this conformer must have C2 symmetry [158].

Frey JA, Muller A, Frey HM, Leutwyler S (2004) Infrared depletion spectra of 2-aminopyridine center dot 2-pyridone, a Watson-Crick mimic of adenine center dot uracil. J Chem Phys 121 8237-8245... 

Figure 21. Fragmentation rates of Na3 C state vibrational bands versus excitation energy [22]. Insert Highly resolved TPI (lower) and depletion spectrum (upper) of the Na3 C state...

Recently25, some new tools have offered very important supports to infrared spectroscopy, as reported in the following instances. The infrared depletion spectrum of the aniline dimer, formed in a supersonic jet, indicates44,45 that two NH2 groups are equivalent. One possible structure is a sandwich, with the N—H n hydrogen bonds, with two aniline molecules arranged head to tail, as shown in 1. 

The typical REE pattern of end-member hydrothermal fluids exhibits a strong enrichment of TREE and a pronounced positive Eu anomaly (Michard et al. 1983 Campbell et al. 1988c Michard 1989 Fig. 13.12), in contrast to the source rocks (MORE) which have a nearly flat, TREE depleted spectrum, and to seawater which is characterized by a strong negative Ce anomaly. The overall pattern is strongly influenced by leaching of plagioclase from MORE under hydrothermal conditions. 

Figure 2-10. Comparison for the depletion spectrum of Na4 and SCF-CI energies for optically allowed states and the oscillator strengths, / for a) rhombic Na4 (singlet state) and b) deformed tetradron Na4 (triplet state). The good agreement with the rhombic structnre lends confidence to the assignment of this geometrical structure. Reproduced with permission from [25]. Copyright 1991 American Chemical Sodety.

Fig. 4.3. Highly resolved TPl lower) and depletion spectrum (DS, upper) of the Nas C state (according to [374]). The vibrational bands are labeled u = 0,1 to 4, but note that v is not a vibrational quantum number...

Fig. 7.9. (a) single laser depletion spectrum of the Oq origin of tetracene in He droplets,... 

Figure 3 A two-colour fluorescence depletion spectrum of one rovibronic line associated with the D n <- A n transition in SO. The two-colour excitation scheme used (upper right) is required because of the very short lifetime (100 fs) of the D P state. This results in the linewidth of 50 cm- shown in the spectrum.

Vj = 1 <— v" = 1 transition will be at a different energy than the Vj = 0 <— v" = 0. We use this fact to measure the vibrational spectrum of V (OCO) in a depletion experiment (Fig. 12a). A visible laser is set to the Vj = 0 Vj = 0 transition at 15,801 cm producing fragment ions. A tunable IR laser fires before the visible laser. Absorption of IR photons removes population from the ground state, which is observed as a decrease in the fragment ion signal. This technique is a variation of ion-dip spectroscopy, in which ions produced by 1 + 1 REMPI are monitored as an IR laser is tuned. Ion-dip spectroscopy has been used by several groups to study vibrations of neutral clusters and biomolecules [157-162]. 

Figure 12. Vibrational action spectra of V (OCO) in the OCO antisymmetric stretch region, (a) Spectrum obtained by monitoring depletion in the photofragment produced by irradiation at the vibronic origin at 15,801 cm The IR absorption near 2391.5 cm removes molecules from V[" = 0, leading to an 8% reduction in the fragment yield, (b) Spectrum obtained by monitoring enhancement in the VO+ photofragment signal as the IR laser is tuned, with the visible laser fixed at 15,777 cm (the Vj = 1 v" = 1 transition). The simulated spectrum gives a more precise value of the OCO antisymmetric stretch vibration in V" (OCO) of 2392.0 cm .

The vibrational teiaperatnre does not change appreciably until we reach spectrum 10 in the sequence shown in Figure 1, i.e., until oxygen depletion has nearly stopped the reaction. Our crude estimate of the vibrational temperature based on the centroid position and the assumption that all vibrational temperature are the same suggests that the vibrational temperature, like the rotational teia-perature, falls below the surface temperature. This cannot be the case because the emission intensity would be too low to detect in our system if the asymmetric temperature were in fact that low. Our Interpretation 1 that symmetric stretch and bending have cooled to the point where they make very little contribution to the emission,... 

Figure 13.10 Partial 9.4 T MALDI-FTMS spectrum of E. coli JM109, showing differences in observable desorbed proteins between natural abundance and isotopically depleted growth media.

The comparison of coronal and photospheric abundances in cool stars is a very important tool in the interpretation of the physics of the corona. Active stars show a very different pattern to that followed by low activity stars such as the Sun, being the First Ionization Potential (FIP) the main variable used to classify the elements. The overall solar corona shows the so-called FIP effect the elements with low FIP (<10 eV, like Ca, N, Mg, Fe or Si), are enhanced by a factor of 4, while elements with higher FIP (S, C, O, N, Ar, Ne) remain at photospheric levels. The physics that yields to this pattern is still a subject of debate. In the case of the active stars (see [2] for a review), the initial results seemed to point towards an opposite trend, the so called Inverse FIP effect , or the MAD effect (for Metal Abundance Depletion). In this case, the elements with low FIP have a substantial depletion when compared to the solar photosphere, while elements with high FIP have same levels (the ratio of Ne and Fe lines of similar temperature of formation in an X-ray spectrum shows very clearly this effect). However, most of the results reported to date lack from their respective photospheric counterparts, raising doubts on how real is the MAD effect. 

The difference in the Li abundances in the G-stars of the Pleiades and the Sun, combined with the probable similarities in their overall chemical composition tell us that PMS Li depletion cannot be the whole story. Another mechanism, additional to convective mixing, must be responsible for Li depletion whilst solar-type stars are on the main-sequence. Recent PMS models that have their convective treatments tuned to match the structure of the Sun reproduce the mass dependence of Li depletion, but deplete too much Li compared with the Pleiades, and can even explain the solar A (Li) in the case of full spectrum turbulence models [9]. The over-depletion with respect to the Pleiades gets worse at lower masses. Better fits to the Pleiades data are achieved with PMS models that feature relatively inefficient convection with smaller mixing lengths. 

---