Photodissociation action spectrum

Fig. 2. The optical absorption spectrum of Ag4+ obtained by the measurement of photodissociation action spectrum. The dots show experimental data the solid line is for eye-guide. The temperature of the cluster ion was estimated to be below 150 K. The transitions are attributed to one-electron transition between the ground and excited electronic states. ...

Fig. 5. The optical absorption spectrum and the electronic structure of Vs" ", (a) Experimental data, where a photodissociation action spectrum of a rare-gas complex, Vs+Ar, was measured by observing a photofragment, Vs+. (b) Density-functional calculation of the spectrum for the most stable isomer illustrated in the inset. The bars show oscillator strengths the solid line a spectral profile, (c) Density-of-states profiles of the majority or and the minority-spin electrons obtained by the density-functional calculation. The shadows indicate occupied electronic levels. The vanadium pentamer ion. Vs" ", was shown to be in the spin triplet state with a trigonal bipyramid structure, where the average bond length was 2.4...

Cheng and coworkers have examined the photodissociation spectroscopy of MgCH4 in detail . The photofragmentation action spectrum has a broad featureless continuum ranging from 310 to 342 nm, with a maximum at 325 nm. In this region the channels observed are nonreactive (equation 36, ca 60%), H abstraction (equation 37, ca 1%) and CH3 abstraction (equation 38, ca 33%). Recent theoretical calculations on the C—H bond activation in MgCH4+ reveal that the formation of the insertion intermediate, CH3MgH, proceeds via a three-centered transition state . ... 

Fig. 1 Infrared photodissociation action spectra in the fingerprint infrared region Irom fairly early in the modem evolution of spectroscopy of biologically interesting complex ions. These spectra illustrate the use of electrospray ion production, ion trapping mass spectrometry (Fourier-transform ion cyclotron resonance in these examples) and the FELIX free electron laser light source. Lower spectrum originally derived from [10, 11] middle spectrum frran [12] upper spectrum from [13]. Figure reproduced with permission from [12]...

The insulating action of the —CH2— group between the phenyl ring and the amino radical in benzylamine can be inferred from another group of experiments. It is well known that under vacuum u.v. irradiation of NH3 and the aliphatic amines the emission spectrum of the excited NH2 radical (a-band system) has been observed.26 Attempts in this laboratory to produce the same luminescent photodissociation in aniline vapor have so far failed. On the other hand, in benzylamine vapor the bands of the -NHj radical are easily observed on illumination by light in the vacuum u.v. range.31... 

It has been shown that acetylene when submitted to a high frequency electric discharge yields some diacetylene 75. The action of ultra-violet radiation of wavelength 2,378-2,100 A on acetylene also produced diacetylene, and Cherton considered that the primary step must be the photodissociation of acetylene to C2H and H. At sufficient pressure the absorption spectrum of acetylene shows a continuous absorption in this region superimposed in the band structure. This gives an upper limit of 121 kcal to D(HC C-H). 

The last reaction is an important source of OH radicals in the troposphere. Hydroxyl radicals do not undergo reactions with any of the major constituents of air, but they react rapidly with many trace compounds and represent the most significant oxidant in the troposphere. Up to 25% of the 0( D) atoms are converted to OH under favorable atmospheric conditions. The spectral window available for the production of 0( D) and OH radicals is quite narrow. Toward short wavelengths, it is limited by the cut-off of the solar spectrum near 300 nm at wavelengths near 320 nm, it becomes ineffective by the diminishing quantum yield for 0( D) formation in the photolysis of ozone. Figure 1 illustrates the overlap between solar radiation intensity, the O3 absorption spectrum, and the 0( D) quantum yield. The area underneath the action curve shown at the bottom of the figure represents the photodissociation coefficient... 

---