Two-photon photoelectron

Figure 9.50 Processes involved in obtaining (a) an ultraviolet photoelectron spectrum, (b) a zero kinetic energy photoelectron (ZEKE-PE) spectrum by a one-photon process and (c) a ZEKE-PE spectrum by a two-photon process in which the first photon is resonant with an excited electronic state of the molecule...

More commonly, the resonant two-photon process in Figure 9.50(c) is employed. This necessitates the use of two lasers, one at a fixed wavenumber Vj and the other at a wavenumber V2 which is tunable. The first photon takes the molecule, which, again, is usually in a supersonic jet, to the zero-point vibrational level of an excited electronic state M. The wavenumber of the second photon is tuned across the M to band system while, in principle, the photoelectrons with zero kinetic energy are detected. In practice, however, this technique cannot easily distinguish between electrons which have zero kinetic energy (zero velocity) and those having almost zero kinetic energy, say about 0.1 meV... 

Figure 9.51 A zero kinetic energy photoelectron (ZEKE-PE) resonant two-photon spectrum of 1,4-difluorobenzene in which the first photon excites the molecule of the zero-point level of the S-[ excited electronic state of the molecule. (Reproduced, with permission, from Reiser, G., Rieger, D., Wright, T.G., Muller-Dethlefs, K. and Schlag, E.W., J. Phys. Chem., 97, 4335, 1993)...

The photoelectronic properties of poly(dihexylgermane) were investigated by photoluminescence spectroscopy, after one- and two-photon absorption. The spectra were compared with those of the analogous poly(dihexylsilane)111. 

The nuclear quadrupole resonance absorption spectra of 2,2 -bipyridine and 4,4 -bipyridine have been measured, and the photoelectron spectra of the same bipyridines and 2,2 6, 2"-terpyridine have been investigated. Two-photon absorption spectra of 2,2 -bipyridine have been taken. ... 

In the experiment, we measured photoelectron spectra from strong-field excitation and simultaneous two-photon ionization of K atoms with BWL (unmodulated) IR pump pulses, as a function of the pulse energy W [68]. The results for energies ranging from W = 0.35 to 2 pj are shown in logarithmic representation in Figure 6.13. All photoelectron spectra exhibit the AT doublet as a signature of the... 

In our experiment a sequence of two intense laser pulses is used to excite K atoms in an atomic beam from the 4.s- to the 4p state. Simultaneously, the pulses ionize the excited a-toms from the 4/7 state to the continuum via two-photon ionization (Fig. 1). Photoelectron spectra were taken at various delay times between the two laser pulses and at different laser intensities at a fixed delay time. 

Leahy, D.J., Reid, K.L. and Zare, R.N. (1991). Effect of breaking cylindrical symmetry on photoelectron angular distribution resulting from resonance-enhanced two-photon ionization, J. Chem. Phys., 95, 1746-1756.,... 

Complete description of two-photon (1 + 1) ionization of NO deduced from rotationally resolved photoelectron angular distribution, ibid, 1757-1767. 

Absorption cross-section for a two-photon transition in 372 the A X, u = 0 <— X n,u" = 0 system of NO Photoelectron spectra resulting from the four-photon 373 (24-2) REMPI of NO via the state... 

---