Photodissociation spectrum

Buck U, Gu X, Lauenstein C and Rudolph A 1988 Infrared photodissociation spectra of size-selected (CHjGH) clusters from / = 2 to 8 J. Phys. Chem. 92 5561... 

Figure 9. Photodissociation spectra of the insertion intermediate of the FeO + CH4 reaction. Top [HO—Fe—CDs], middle [HO—Fe—CHs], bottom (dashed) Franck-Condon simulation of the [HO—Fe—CHs] spectrum. The spectrum shows a long progression in the Fe-C stretch (Vii = 478 cm ) and short progressions in the Fe—O stretch (vg = 861 cm ) and O—Fe—C bend (V14 = 132 cm ).

Figure 16. Experimental and calculated IR resonance enhanced photodissociation spectra of Fe" (CH4)3 and Fe" (CH4)4. Experimental spectra were obtained by monitoring loss of CH4. Calculated spectra are based on vibrational frequencies and intensities calculated at the B3LYP/ 6-311+G(d,p) level. Calculated frequencies are scaled by 0.96. The calculated spectra have been convoluted with a 10-cm full width at half-maximum (FWHM) Gaussian. The D2d geometries of Fe (CH4)4 are calculated to have very similar energies, and it appears that both isomers are observed in the experiment.

The photoactivation of Mg(L)+ complexes of organohalogens has been widely studied . The photodissociation spectra of the methyl halide complexes, Mg(XCH3) (where X = F, Cl, Br and I), have been studied in great detail by Furuya and coworkers in two publications . Each of the four halides exhibits spectra with three absorption bands at the red and blue sides of the free Mg+ 2S transition. These three absorption... 

The photodissociation spectra of Mg(CH30H) + complexes has been studied as a function of cluster size, For n = 1, the main reaction channels involve formation of Mg+ (cf equation 39) and MgOH+ (cf equation 43). Small amounts of CH3+ (cf equation 41)... 

Photodissociation of the Mg+" complex of pyridine yields two products Mg as the major product (cf equation 39) and C5H5N+ via electron transfer (cf equation 40) as the minor channel . The photodissociation spectra of Mg(NCCH3) complexes has been... 

The photodissociation spectra of the Mg(L) complexes of ethyl isocyanate and ethyl isothiocyanate show some common photofragments. Aside from the ubiquitous formation of Mg+ (cf equation 39), both ethyl isocyanate and ethyl isothiocyanate yield products from attack of the N—C single bond (equations 57 and 58). The ethyl isothiocyanate complex also yields MgS via equation 59. The photodissociation spectrum of the ethyl thiocyanate isomer was also examined and gave the products shown in equations 60-62. Thus each isomer gives a unique ionic product [Mgs for ethyl isothiocyanate (equation 59) vs MgNC+ for ethyl thiocyanate (equation 62)] which allows their distinction. Finally, the Mg(ethyl isocyanate) +" complexes simply undergo solvent evaporation for n = 2 and 3 (cf equation 52). 

Although the pulse duration of the valve was 2 ms, the high pressure of the reagent gas had a rise time of about 200 ms and was pumped away by a high speed 5 in. diffusion pump in approximately 400 ms. Swept double resonance pulses were then used to isolate the ion of interest, which was subsequently trapped for 3 6 seconds (determined by the ion s cross section for photodissociation) either in the presence or absence of radiation. For each ion, two sets of,photodissociation spectra were taken, one at 2 x 10 ° torr argon, to permit collisional cooling, and another at a background pressure of 10 torr [28]. In all cases, data from the collisionally cooled ions are presented. 

Photodissociation spectra were obtained by monitoring the appearance of ionic photoproducts as a function of the wavelength of light. Shot-to-shot variation of the lasergenerated metal precursor ions made monitoring the photodisappearance of the parent ion impractical. Assuming a one-photon process [17 29]- the photodissociation of AB+, eq. 1, can be described by first-order kinetics, eq. 2,... 

Finally, although the information content of these photodissociation spectra is great with regard to ion structure and thermochemistry, the high density of low lying electronic states makes band assignments virtually impossible at this time. In fact such an interpretation will provide a real challenge to theorists for years to come. 

One of the first examples from our laboratory [13] which suggested that photodissociation thresholds could yield quantitative metal-ligand bond energies was from a comparison of the photodissociation spectra of FeOH+ and FeC0+ obtained by monitoring reactions 9 and 10, respectively, and shown in Figure 3 The two spectra are remarkably similar with two absorption maxima observed... 

Ni, Cu, Nb, Ta). To summarize those results, both M+ and Fe are observed as photoproducts, with the metal having the lowest ionization potential predominating. The photodissociation spectra reveal broad absorption in the ultraviolet and visible regions with a range of cross sections from 0.06 A2 for VFe+ to 0.62 A2 for for CrFe+. Bond energies obtained by observing photoappearance onsets are in the range of 48 kcal/mol for ScFe+ to 75 kcal/mol for VFe+ (see Table I). These studies can be readily extended to other dimer series, such as MV+,... 

The photodissociation spectra of all of the ions showed no pressure dependence, except for slight quenching of the low energy tail region, indicating that photodissociation in these cases is probably due to one-photon excitation and that the precursor Ions do not have substantial internal energy. 

NO(2E, n j ) and monitors the total fluorescence from the excited electronic state of NO as a function of the photolysis wavelength A which was used to excite the C1NO parent molecule to the T state. If properly normalized, the photofragment yield spectra correspond to the partial photodissociation spectra discussed in Section 1.4.6. In view of (7.23) and Figure 7.6 the a(X,n,j) have the same resonance behavior as the total spectrum. The upper part of Figure 7.14 depicts three examples for various final vibrational states n the rotational state of NO varies between 1.5 and 4.5. (Because of the electronic spin of NO, the rotational quantum number j is half-integer in this case.)... 

In addition to UV/visible flash photolysis and TRIR spectroscopy, other techniques have been used for the detection of transition metal-noble gas interactions in the gas phase. The interaction of noble gases with transition metal ions has been studied in detail. A series of cationic dimeric species, ML" " (M = V, Cr, Fe, Co, Ni L = Ar, Kr, or Xe), have been detected by mass-spectroscopic methods (55-58). It should be noted that noble gas cations L+ are isoelectronic with halogen atoms, therefore, this series of complexes is not entirely unexpected. The bond dissociation energies of these unstable complexes (Table IV) were determined either from the observed diabatic dissociation thresholds obtained from their visible photodissociation spectra or from the threshold energy for collision-induced dissociation. The bond energies are found to increase linearly with the polarizability of the noble gas. 

Photodissociation of the dimer [2-2] to the pyridinyl radical (2 ) occurs readily in thin films at low temperatures or in acetonitrile solutions. Although excitation spectra could not be obtained from these experiments a new technique was used 1) the wavelength dependence of radical formation from dimer generated electro-chemically in small amounts, 2) the measurement of the radical produced by a rapid jump to a potential at which reoxidation of the radical takes place. Since the photodissociation spectra of dimers may well determine their practical use, a convenient procedure is useful. 

Given the fact that we have observed photodissociation from "hot bands" of the sodium trlmer, it should be possible to alleviate this hot band structure and in this way obtain photodissociation spectra which result only from the pumping of bound-free transitions involving cooled sodium trlmer. 

Farrar and co-workers recorded the photodissociation spectra of the isoelectronic Sr+-(NH3) system and observed similar large spectral shifts for the 5 P-5 S transition [25, 26]. They carried out a moment analysis of the absorption spectra and found a large increase in the electronic radial distribution in the ground state with... 

These and more complex clusters [aniline/(H20) ]+, n = 1-8 are investigated by infrared photodissociation spectra supplemented by density functional theory calculations196. Scheme 22 gives the calculated geometries in the case of n = 4. 

The N—H N hydrogen bond is responsible for the formation of the complexes between aniline and aliphatic amines (ammonia, methylamine, dimethylamine and tri-methylamine) which act as proton acceptors. Infrared photodissociation spectra and DFT calculation indicate208 that the clusters [aniline/ammonia]+ and [aniline/methylamine]+ have a non proton transferred (without the proton donation from the aniline moiety to the amine molecule) structure, while the complexes [aniline/dimethylamine]+, [aniline/ trimethylamine]+ possess a proton transferred structure. Reasonably, the proton transfer increases on increasing the proton affinity of the amine used as solvent. 

IR data were reported for size-selected H+(H20)n clusters, where n = 6 - 27.619 Argon photodissociation spectra gave vOH values for Cl2. nII2C). For n = 1 or 2, the presence of a single band suggests that the H20 molecules bond symmetrically to the ion.620 The IR spectra of argon-solvated X. IIDO species, where X = F or I, show that they are preferentially F. HOD, I. DO I respectively.621 DFT and ab initio calculations gave vibrational wavenumbers for CsOH(H20)n, where n = 0 - 4.622... 

Molecular Oxygen, Peroxo, Aquo and Related Complexes. Ab initio calculations have been reported for vibrational wavenumbers for M+(H20)n, where M = Li, Na, K, Rb or Cs n = 1-6.320 vOH mode assignments were proposed from the IR photodissociation spectra of gaseous Mg(H20)4+ and [Mg(H20)4Ar]+ (3000-3450 cm ).321... 

Mass-selected IR photodissociation spectra of V+(H20)Arn and V+(D20)Arn clusters show vOH bands shifted by 50-80 cm-1 to lower wave-numbers compared to free H20.324 The peroxo group in [ Ph3Si0 2Vv0(02)] shows vOO at 872 cm-1.325 A similar feature was seen at about 920 cm" 1 in the IR spectrum of [V0(02)(CMAA)(H20)]2, from the p -peroxo ligand.326 IR... 

IR photodissociation spectra were reported for the clusters Al+(C02)n and Al+(C02)n.Ar, and compared with the results of ab initio calculations (all in the region of vasC02 modes).378 The complex (68), where R = 2,4,6-Ph3C6H2, has vCO at 1624 cm-1, compared to 1696 cm-1 in the free ligand, confirming the coordination shown.379 There is IR evidence for the formation of bi- and poly-dentate carbonato complexes by the adsorption of gaseous C02 on to (t-Ga203.380... 

Laser-ablated magnesium atoms react with MeOH to form matrix-trapped Mg(MeOH), with the assignments listed in Table 9.391 IR photodissociation spectra of gaseous Mg(MeOH)n+, where n = 1 4, gave assignments to vOH (assigned using DFT calculations).392... 

Other hand, the potential success of laser selective chemistry depends on the existence of metastable vibrational energy distributions. Structural information about the nature and effects of the weak bonding interaction are obtained from spectral shifts, intensities and, in favorable cases, rotational structure in the photodissociation spectra. Rotational structure, vibrational frequencies and band intensities are all influenced by the intramolecular potential. 

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