Resonance-Enhanced Multiphoton Ionization REMPI Spectra

5 Resonance-Enhanced Multiphoton Ionization (REMPI) Spectra 

Values in parentheses represent the likely uncertainty in interpolating between the Ne calibration lines. - One standard deviation in parentheses. 

It may be noted that early REMPI studies of NH3 in the range 380 to 500 nm identified 

Values in parentheses represent the probable uncertainty in interpolating between the Ne calibration lines. - One standard deviation in parentheses. - Hot bands from a A, v=1 (and v = 2 for j A of ND) were also observed. - From a wavelength scan of the total electron current in REMPI-PES study [9]. - From analysis of hot bands. 

NH -NH Transitions. The REMPI-PES technique allows selection of a single rovibra-tional level (v, N, J ) in the resonant Rydberg state so that only a few levels of the ion (v, are accessed this procedure substantially simplifies the PES (compared with 

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Rydberg States. Vibrationally and rotationally resolved, (2 +1)-resonance-enhanced multiphoton ionization (REMPI) spectra and REMPI-PES of NH, ND(a A) and NH, ND(X S ) radicals in the UV (cf. pp. 83/7) revealed the existence of some singlet and triplet Rydberg states. Using literature data for the spectroscopic constants of the a and states,... 

The intensities of resonance-enhanced multiphoton ionization (REMPI) spectra suggest that the population of nascent N2 in the vibrational ground state is larger than in the first excited state [44]. A rotational maximum of N2 in the ground state at J = 70 and a width AJ of 18 (FWHM) were determined at 248 nm [45]. The intensities of REMPI spectra yielded a maximum of the rotational population of N2 in the ground state at with a spread... 

Until recently gas phase studies have been limited to molecules that can be heated without degradation. For the nucleobases this includes adenine (A), but not, for example guanine (G) and none of the nucleosides. Since the first report of the resonance enhanced multiphoton ionization (REMPI) spectrum of laser desorbed guanine in 1999, laser desorption has essentially rendered all bases and their clusters amenable to study as neutral species in the gas phase [3],... 

In a resonance enhanced multiphoton ionization (REMPI) spectrum the differential cross section may be expanded in Legendre polynomials, but this expansion does not collapse to a single term. For (n + m) REMPI ... 

Infrared diode laser absorption spectroscopy has been employed to detect ground-state SiH2 and allowed the first observation of its high-resolution IR spectrum by Yamada and coworkers in 1989 . State-selective multiphoton IR excitation of SiH2 has been examined computationally . The resonance-enhanced multiphoton ionization (REMPI) spectrum of SiH2 was observed for the first time by Robertson and Rossi and was employed to measure the SiH2 sticking coefficient on a silicon surface . ... 

The vibration spectrum of the first excited state of guanine was measured using laser desorption jet-cooled resonance-enhanced multiphoton ionization (REMPI) spectrometry <1999JA4896>. The millimeter wave spectrum of purine was collected using a free jet spectrometer, and the observed rotational spectrum was assigned to the N(9)-H tautomer <1996CPL189>. 

More detailed investigations [118] included a deeper look at the SO rovibrational spectrum and a resonance enhanced multiphoton ionization (REMPI) analysis of the methyl radicals. These resulted in total rovibrational energies for the fragments. The translational energy component was not measured. The quantum yield for formation of SO in its ground electronic state ( Z) was unity within experimental error. Evidence for two types of methyl radicals, as might be expected for stepwise decomposition, was not found, so the authors suggested that the three-body dissociation pathway was dominant [118]. 

In solution the keto forms dominate. In matrix-isolation IR observation of C=0 stretch, frequencies points to keto forms but too many lines are present in the spectra to be able to exclude other tautomers as well [28]. The same problem manifests itself in resonance-enhanced multiphoton ionization (REMPI or R2PI) spectroscopy, where a dense spectrum is observed that potentially consists of contributions of multiple tautomers [29], These contributions can be separated by UV-UV hole-burning, revealing the presence of four different isomers in the gas-phase jet-cooled conditions of these experiments [30]. Three of these tautomer-selective REMPI spectra appear in Figure 7.3. Further identification is possible by IR-UV hole burning and by tautomeric blocking with methyl derivatives [30-32]. The spectra of species A (with the red-most origin at... 

Figure 12 Raman-REMPI (resonantly enhanced multiphoton ionization) spectrum of the °Qi(AJ = 0, AK = -2,K- 1) transitions of the Vie e2g) mode of benzene in a molecular beam. An energy-level diagram is shown for the double-resonance experiment. The ultraviolet source was tuned to 36,474 cm and the Raman wave-number calibration is adjusted to match the / = 6 line reported in Ref. 109. The expansion was 13% benzene in argon at 80 kPa and the sampling was done at XfD = 175 (D = 0.20 mm nozzle diameter) using pump and Stokes laser energies of 2 and 0.5 mJ. (From Ref. 117, with permission.)...

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