IR multiphoton excitation

Figure A3.13.2. Illustration of the analysis of the master equation in temis of its eigenvalues and example of IR-multiphoton excitation. The dashed lines give the long time straight line luniting behaviour. The fiill line to the right-hand side is for v = F (t) with a straight line of slope The intercept of the...

Quack M and Sutcliffe E 1983 Quantum interference in the IR-multiphoton excitation of small asymmetric-top molecules ozone Chem. Phys. Lett. 99 167-72... 

Herve S, Le Quere F and Marquardt R 2001 Rotational and vibrational wave packet motion during the IR multiphoton excitation of HF J. Chem. Phys. 114 826-35... 

The record m the number of absorbed photons (about 500 photons of a CO2 laser) was reached with the CgQ molecule [77]. This case proved an exception in that the primary reaction was ionization. The IR multiphoton excitation is the starting pomt for a new gas-phase photochemistry, IR laser chemistry, which encompasses numerous chemical processes. 

Early laser Isotope separation after IR multiphoton excitation high selectivity at room temperature... 

The most exciting application of bond order indices concerns the description of chemical reactions involving the simultaneous change of several bonds. An example is the unimolecular decomposition of ethanol, which can happen at high temperature or IR multiphoton excitation of the molecule. Out of the possible dissociation channels, the lowest barrier characterizes the concerted water loss of the molecule, yielding ethene and H20 [30]. 

Finally, the gas-phase behavior of the enolate anion of dimethylsilanone has been investigated. This anion was produced by collision-induced dissociation389 or IR multiphoton excitation390 of Me3SiO" and by IR multiphoton excitation of Me2HSiO 390 The upper limit of 62 kcal mol"1 has been deduced for the strength of the n part of the Si=Q bond from these experiments390. 

Molecular photodissociation can also be achieved by IR multiphoton excitation. A classical example of such processes is that of SFs + nhi/ SF5 + F, which can also be applied to produce isotope enrichment in a SFg/ SFe mixture (the mechanism for this process is discussed in some detail in Chapter 18). 

In addition, new tandem mass spectrometry technologies were also among the important innovations. Apart from traditional collision-induced dissociation (CID) [89-91], a variety of activation methods (used to add energy to mass-selected ions) based on inelastic collisions and photon absorption have been widely utilized. They include IR multiphoton excitation [92,93], UV laser excitation [94—97], surface-induced dissociation (SID) [98-100], black body radiation (101, 102], thermal dissociation [103], and others. As the fragmentation of peptide/protein ions is a central topic in proteomics, there is strong interest in such novel ion dissociation methods as electron capture dissociation (ECD) [104, 105] and electron transfer dissociation [22]. These new methods can provide structural information that complements that obtained by traditional collisional activation. Also, very recently, ambient ion dissociation methods such as atmospheric pressure thermal dissociation [106] and low temperature plasma assisted ion dissociation [107] have been reported. 

Fig. 10.5 Schemes for resonance molecular photoionization via high-lying vibrational states by way of multiphoton resonance vibrational excitation with IR laser radiation (a) multiphoton IR + VUV excitation, (b) IR multiphoton excitation, and (c) IR multistep + VUV excitation.

Kohno, j. T Toyama, N. Buntine, M. A. Maeune, F Kondow, T. Gas phase ion formation from a liquid beam of arginine in aqueous solution by Ir multiphoton excitation. Chem. Phys. Lett. 2006, 420(1-3), 18-23. 

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