4s Rydberg States Research Articles

Mechanisms of Multiphoton Bleaching of Red Fluorescent Proteins

Two-photon laser scanning microscopy (TPLSM) has several advantages over one-photon confocal microscopy, including deeper tissue penetration, higher signal-to-background ratio, and less photodamage in the out-of-focus volume. However, due to very high instantaneous light intensities in the focal volume, the probability of further, stepwise resonant photon(s) absorption increases dramatically, leading to very efficient bleaching of a probe. To deal with this challenge one has to understand the underlying mechanisms. Here we measured the power dependence of multiphoton bleaching rates of several red fluorescent proteins expressed in live E. coli cells under two-photon microscope conditions. To clarify the photophysical mechanisms, we also used much lower repetition rate (1 kHz) and different pulse durations in experiments in vitro with Ti:Sa amplifier excitation. Our experimental data supported by quantum mechanical calculations of the chromophore in protein environment are consistent with the mechanism of ultrafast (<150 fs) singlet-singlet stepwise absorption of one or two additional photons following initial simultaneous two-photon absorption. In the DsRed2 protein, the third photon absorption most probably results in an ultrafast electron transfer (ET) from the anionic chromophore to an excited Rydberg state of a nearby positive amino acid residue (e.g. K163+). The transient radical state of the chromophore tends to accept an electron from the deprotonated E215- amino acid, thus promoting the first step of the recently established decarboxylation reaction. In mFruits proteins, the third photon promotes an ET from the chromophore to the 4S Rydberg state of nearby K70+ residue with its subsequent photoionization by the fourth photon.

Electronic spectroscopy of the Ẽ← X̃ transition of NO–Kr and shielding/penetration effects in Rydberg states of NO–Rg complexes

We report the results of a (2+1) resonance-enhanced multiphoton ionization (REMPI) study of the E2Sigma+(4ssigma) Rydberg state of NO-Kr. We present an assignment of the two-photon spectrum based on a simulation, and discuss it in the context of previously-reported spectra of NO-Ne and NO-Ar. In addition, we report on spectra in the region of the vNO=1 level of the E, F and H' 4s and 3d Rydberg states of NO-Rg (Rg=Ne-Kr). Since the NO vibrational frequency is affected by electron donation from the rare-gas (Rg) atom to the NO+ core, as well as by the penetration of the Rydberg electron, the fundamental NO-stretch frequency reflects the interactions in the complex. The results indicate that the 4s Rydberg state has a strong interaction between the NO+ core and the Kr atom, as was the case for NO-Ar and NO-Ne. For the 3d Rydberg states, although penetration is not as significant as for the 4s Rydberg states, it does play an important role, with subtle angular effects being notable.

Electronic spectroscopy of NO–(Rg)x complexes (Rg=Ne,Ar) via the 4s and 3d Rydberg states

We have employed (2 + 1) resonance enhanced multiphoton ionization spectroscopy to investigate the 3d and 4s Rydberg states of the NO molecule when bound to the surface of Rg(x) clusters (Rg = rare gas). We observe that the spectra of the NO-Ar(x) species converge in appearance as x increases, and this is discussed in terms of two Rg atoms interacting with the NO+ core, with other Rg atoms being "outside" the Rydberg orbital. We show that the interaction of each of the Rg atoms with the NO is essentially independent for the NO-Rg2 complexes: both by comparing our spectra for Rydberg states of NO-Rg and NO-Rg2, and from the results of ab initio calculations on NO+ - Rg and NO+ - Rg2. In addition, we discuss the disappearance of some electronic bands upon complexation in terms of Franck-Condon factors that are very sensitive to the angular coordinate. We relate our results to those of the bulk by comparing to the previously reported electronic spectroscopy of NO in both Rg matrices and He nanodroplets.

Study on the resonance-enhanced multiphoton ionization of the 4s and C̃ states of SF2 radicals

Abstract SF 2 radicals were generated by using a pulsed dc discharge in a mixture of SF 6 /Ar. The (2+1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy of SF 2 radical was observed between 320 and 365 nm. The analysis shows that the observed spectra can be assigned as the resonant excitation of the SF 2 radical (the 4s Rydberg state and C state). The spectroscopic parameters ω 1 ′ and ω 2 ′ were obtained. We also clarified the dissociative characteristics of the C state and inferred the mechanism of dissociation.

RESONANCE ENHANCED MULTIPHOTON INOIZATION STUDIES OF CF2Cl RADICALS BETWEEN 332nm AND 362nm

The (2+1) resonance-enhanced multiphoton ionization (REMPI) spectra of the CF2Cl radicals, which are generated by a pulsed dc discharge,were investigated between 332 and 362nm.Two new Rydberg states,4s and 4p,were observed and indentified.The observed states and spectroscopic constants include 4s Rydberg state (band origin ν0—0=55371cm-1,ω3′ (CF2 scissors)=523±7cm-1,ω′4 (OPLA,i.e.,out-of-plane bending mode)=734±4cm-1) and 4p Rydberg state (ν0—0=57601.3cm-1,ω3′=552±10cm-1,ω4′=762±12cm-1).The quantum defect values of 4s and 4p Rydberg states were also estimated.It seems that the radical production by a pulsed dc discharge combined with PEMPI technique is a powerful tool to study the electronic state of radicals.

Spin–orbit configuration-interaction study of valence and Rydberg states of LiBe

A b initio spin–orbit full configuration-interaction calculations in the context of relativistic effective core potentials are reported for the weakly bound metal dimer LiBe, a three-valence-electron system. The effects of basis set on the energies of valence and Rydberg states of the cluster are discussed, as are the effects of configuration space selection on the energy of the latter states. Results at the dissociative limit are compared to the experimental atomic spectra. Potential-energy curves and spectroscopic constants are presented for the ground state and fourteen excited states, which includes the Li and Be 2p valence states, the Li 3s, 3p, 3d, and 4s Rydberg states, as well as three low-lying states of the molecular cation.

Potential energy curves of the ground, excited, and ionized states of Ar2 studied by the symmetry adapted cluster-configuration interaction theory

Symmetry adapted cluster-configuration interaction theory is applied to the calculation of potential energy curves for the ground, excited, and ionized states of Ar2. The excited states studied here dissociate into Ar(3p6)+Ar(3p54s1) and Ar(3p6)+Ar(3p54p1). Spin–orbit coupling is included by a semiempirical method. The present results, especially for the 4s Rydberg states, compare very well with the experimental results of absorption and emission spectra. Some new assignments of the observed spectra are given, particularly for excitations from bound excited states of Ar2.

MRD CI calculations of excited states of the SiH 3 radical, including potential curves for the inversion mode and the dissociation SiH 3 → SiH 2 + H

Using the MRD CI method and large basis sets the vertical spectrum of silyl radical (SiH 3) has been calculated. The lowest excited state is the 4s Rydberg state, 41000 cm −1 (5.2 eV) above the ground state. Only one excited valence state (2 2E) was encountered, all other states are of Rydberg type. From potential curves for the inversion mode (symmetric bending motion) it was inferred that all Rydberg states are planar, whereas the valence excited state is highly pyramidalized. The investigation of the dissociation reaction SiH 3 → SiH 2 + H leads to the conclusion that the first excited state is dissociative.

ChemInform Abstract: ELECTRONIC SPECTRA OF BUTADIENE AND ITS METHYL DERIVATIVES: A MULTIPHOTON IONIZATION STUDY

The multiphoton ionization (MPI) spectra of trans‐1,3‐butadiene and three of its methyl substituted derivatives have been recorded using a tunable visible dye laser. The effect of methyl substitution on the electronic structure of butadiene is investigated, resulting in a reassignment of the spectra of these molecules. Quantum defects are found to be independent of principal quantum number, indicating little mixing between Rydberg and core orbitals. The validity of retaining conventional s, p, d, and f descriptions of Rydberg orbitals in these quasilinear molecules is demonstrated. Two electronic states of butadiene, assigned to the 3d and 4s Rydberg states, are observed for the first time in optical spectroscopy. No evidence for an excited 1Ag valence state is found in the MPI spectra.

Electronic spectra of butadiene and its methyl derivatives: A multiphoton ionization study

The multiphoton ionization (MPI) spectra of trans-1,3-butadiene and three of its methyl substituted derivatives have been recorded using a tunable visible dye laser. The effect of methyl substitution on the electronic structure of butadiene is investigated, resulting in a reassignment of the spectra of these molecules. Quantum defects are found to be independent of principal quantum number, indicating little mixing between Rydberg and core orbitals. The validity of retaining conventional s, p, d, and f descriptions of Rydberg orbitals in these quasilinear molecules is demonstrated. Two electronic states of butadiene, assigned to the 3d and 4s Rydberg states, are observed for the first time in optical spectroscopy. No evidence for an excited 1Ag valence state is found in the MPI spectra.