Evidence for Rydberg Doorway States in Photoion Pair Formation in Bromomethane (original) (raw)
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Multiphoton Rydberg and valence dynamics of CH3Br probed by mass spectrometry and slice imaging
Physical Chemistry Chemical Physics, 2018
The multiphoton dynamics of CH 3 Br were probed by Mass Resolved MultiPhoton Ionization (MR-MPI), Slice Imaging and Photoelectron Imaging in the two-photon excitation region of 66 000 to 80 000 cm À1. Slice images of the CH 3 + and Br + photoproducts of ten two-photon resonant transitions to np and nd Rydberg states of the parent molecule were recorded. CH 3 + ions dominate the mass spectra. Kinetic energy release spectra (KERs) were derived from slice and photoelectron images and anisotropy parameters were extracted from the angular distributions of the ions to identify the processes and the dynamics involved. At all wavelengths we observe three-photon excitations, via the two-photon resonant transitions to molecular Rydberg states, forming metastable, superexcited (CH 3 Br #) states which dissociate to form CH 3 Rydberg states (CH 3 **) along with Br/Br*. A correlation between the parent Rydberg states excited and CH 3 ** formed is evident. For the three highest excitation energies used, the CH 3 Br # metastable states also generate high kinetic energy fragments of CH 3 (X) and Br/Br*. In addition for two out of these three wavelengths we also measure one-photon photolysis of CH 3 Br in the A band forming CH 3 (X) in various vibrational modes and bromine atoms in the ground (Br) and spin-orbit excited (Br*) states.
Resonance enhanced (2+1) multiphoton ionization spectrum of Br2: The lower Rydberg states
Chemical Physics, 1990
The resonance enhanced (2+1) multiphoton ionization spectrum of Br 2 has been recorded in the region 61000-85000 cm -1 and gerade Rydberg states up to n=11 have been identified. Two series are seen, based on the Ω= 3/2 g and 1/2 g core states. All of the higher states are members of the ns series but four components of the [Ω] 4d multiplet close in energy to [Ω] 6s have been identified for the first time. The quantum defects are very similar to those of the Br atom and to those of the lower members of the d series in CH 3Br. The s series is at least an order of magnitude more intense than the d series, but intensities within each [Ω c] ns←-X and [Ω c]4d←X multiplet present some unexpected features.
High-lying Rydberg states of vinyl bromide studied by two-photon resonant ionization spectroscopy
Chemical Physics Letters, 2004
High-lying Rydberg states of vinyl bromide at 70 000-79 500 cm À1 have been investigated using 2 + 1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. Seven Rydberg series, including one s, three p, two d, and one f, have been identified from fitting the term values of observed electronic states to Rydberg formula rendering the ionization energy of 79 194 ± 17 cm À1 (9.819 ± 0.002 eV). All of the seven series converge to the same ionization-energy limit, corresponding to the ground state of vinyl bromide cation. The adiabatic ionization energy of vinyl bromide determined from this study is in excellent agreement with the values reported recently by other methods.
The Journal of Physical Chemistry A, 2010
Nascent emission and laser-induced dispersed fluorescence spectra of products or intermediates from the multiphoton photolysis reaction of bromomethanes (CHBr 3 , CHBr 2 Cl, CHBrCl 2 , and CH 2 Br 2) at 266 nm were recorded in a slow flow cell. Electronically excited species including CH (A 2 ∆, B 2 Σ-, and C 2 Σ +), C 2 (d 3 Π g), and atomic Br (4 D J and 4 P J) were observed in the nascent emission spectra. Free radicals such CHBr or CHCl were also successfully found using laser-induced dispersed fluorescence spectroscopy. The reactive intermediate, CHBr, was seen only in the photolysis of CHBr 3 , whereas CHCl was only discovered when the precursor was CHBr 2 Cl or CHBrCl 2. More experiments including the power dependence and temporal waveform measurements were conducted. The present study reports the first direct measurements of the intermediate products in the multiphoton photodissociation reaction of these bromomethanes at 266 nm. Nascent emission spectra following the photolysis at longer near-ultraviolet wavelengths (280 and 355 nm) were also acquired. On the bassis of these results, the multiphoton photodissociation mechanism of these bromomethanes at 266 nm can be confirmed.
Chemical Physics, 2006
The threshold photoelectron (TPES) and the photoionization mass spectrometric study of CH 3 Br in the 8-20 eV photon energy range is presented. The interpretation and assignments are supported by ab initio calculations. The TPES shows several new discrete features in the Jahn-Teller split ground state X 2 E(2 A'-2 A") of CH 3 Br +. An additional continuous band starts at about 11.8 eV. These observations are both correlated with direct ionization and autoionizing transitions. This is supported by constant ion state (CIS) spectroscopy. A large enhancement of the transitions to the A 2 A and B E states is ascribed to important autoionizing contributions. Based on the present calculations, the weak to very weak bands in the 17.5-22.0 eV photon energy range were mainly assigned to 2a 1-1 ionization and to double excitations described essentially by the 2e-2 4a 1 1 and le-1 2e-1 4a 1 1 configurations. The photoionization mass spectrometric study allowed us to investigate in detail the ionization and dissociation of CH 3 Br + leading to CH 2 + , CH 3 + , Br + and CH 2 Br + from threshold up to 20 eV photon energy. The experimental data are compared to ab initio dissociation energies. At the onset, the CH 3 + and CH 2 Br + fragment ion production is correlated with the ground state of CH 3 Br + and both fragment ions have to appear through dissociative autoionization from the (3a 1 1 /1e 3)6s or 5s Rydberg state. This interpretation is supported by the photoabsorption spectrum measured recently in the same photon energy range. At higher energies, beside a likely direct (pre)dissociation of the à 2 A 1 and B 2 E states of CH 3 Br + , autoionization also contributes to the fragmentation in all decay channels. Avoided crossings in a manifold of 2 A' states are likely to be involved. This is supported by ab initio calculations. For CH 3 + the photoion-pair process is analyzed and detailed assignments are proposed on the basis of our latest VUV photoabsorption spectroscopic data.
Ultrashort-Lived Non-Rydberg Doubly Excited Resonances Observed in Molecular Photoionization
The N 2 1 ͑B 2 X͒ dispersed fluorescence from photon excited N 2 molecules has been measured in the 19 -34 eV excitation range, where our theory predicts the existence of non-Rydberg doubly excited resonances which autoionize in the sub-fs regime into the N 2 1 B 2 S 1 u ionic state. The experimentally deduced vibrational branching ratios ͑y 0 1͒͑͞y 0 0͒ revealed five prominent features, four of which could be identified as such doubly excited resonances based on the lowest order of the many-body perturbation theory. [S0031-9007(96)00230-X]
Technique to study Rydberg states by multiphoton ionization spectroscopy
Journal of the Optical Society of America B, 1988
A new technique to study the Rydberg states of the barium atom has been developed. In this technique a multiphoton ionization signal is detected by selective excitation of the ground-state ion (6s) to an excited state (6p), which results in a collimated amplified spontaneous emission signal at the 6p-5d transition of Ba+. Discrete Rydberg states, 6snl (1 = 0, 2), as well as autoionizing Rydberg states, 5dnl (I = 0, 2) and 6pnl (= 0, 2) are observed by this novel but simple method.
Molecular Rydberg transitions. Multichannel approaches to electronic states: CH3I
Physical Review A, 1981
A multichannel quantum-defect theoretic (MQDT) analysis of the high-resolution vacuum-ultraviolet spectrum of CH3I in the energetic region below the first ionization limit is presented. The analysis is based upon, and substantiates a posteriori, quantumdefect analogies between Xe and CH3I: that is, only purely electronic molecular channels are allowed to interact. A new d series converging on the first ionization limit is assigned as a result of the MQDT analysis.
Molecular Rydberg transitions. Intermediate coupling in simple bromides
Chemical Physics Letters, 1981
An intermediate coupling analysis of the low-energy 7r ~ a Rydberg transitions of hydrogen bromide, cyanogen bromide, acetylene bromide and alkyl bromides is presented. Exchange and spin-orbit coupling parameters are calculated and their variations discussed. The Br 5s orbital is delocalized in the larger alkyl bromides and Br 4p is heavily involved in lr bonding in acetylene and cyanogen bromides.