Optical-optical Double Resonance Excitation Research Articles

Ion-core switching in Rydberg series of XeKr

We investigate XeKr in high Rydberg states by mass-resolved optical-optical double resonance excitation spectroscopy. We excite XeKr via two-photon absorption to the v* = 0 and v* = 2 vibrational levels of an intermediate electronically excited state of Xe*Kr correlated to Xe*6p[5/2]2 and excite Xe*Kr further via one-photon absorption to the high Rydberg states of Xe**Kr in the energy range of 93200–97400 cm−1. The potential energy curves and the quantum defects of the d-Rydberg and s-Rydberg series of Xe**Kr, converging the A 2Π3/2 state of XeKr+ are determined. From the kinetic energy release in the predissociation process, we conclude that the ion-core switching occurs by the interaction between the bound electronic states of Xe**Kr converging to the A 2Π3/2 state of XeKr+ and the repulsive electronic states of low-lying electronic states of XeKr**. Based on numerical simulations, we interpret the dependence of the yield of the ion-core switching on the excitation energy in terms of the population transfer from the bound electronic states of the high Rydberg states Xe**Kr, converging to the A 2Π3/2 state of XeKr+, to those converging to the electronic ground X2 Σ 1 / 2 + state of XeKr + .

Observations and analysis with the spline-based Rydberg–Klein–Rees approach for the 31Σg+ state of Rb2

Ro-vibrational term values of the 3(1)Σg (+) state of (85,85)Rb2 and (85,87)Rb2 and resolved fluorescence spectra to the A(1)Σu (+) state are recorded following optical-optical double resonance excitation. The experimental data are heavily perturbed, and as a result, the standard analysis based on Dunham series representation of the energy levels fails. The analysis is done via modeling the adiabatic potential function with the Rydberg-Klein-Rees potential constructed from the generalized smoothing spline interpolation of the vibrational energies Gv and rotational constants Bv.

Luminescence of ion-pair I2 (D′) state in cryogenic perfluorocarbons and SF6 solids

Luminescence of I2-doped CnF2n+2 (n = 1–4) and SF6 cryogenic solids has been studied using an optical-optical double resonance excitation technique. Experiments have shown that the lowest ion-pair state I2(D′) is stable with respect to chemical reaction and fast predissociation in these hosts. The red shift of I2(D′ → A′) transition energy relative to the gas phase shows no correlation with the host polarizability and is ∼3500 cm−1 for all studied solids. Besides the I2(D′) solvation energy, a part of the shift is due to a repulsive interaction of I2(A′) with the host molecules. In the CF4 and SF6 solids, the I2(D′ → A′) spectrum shows evidence of a coupling between electronic transition in the guest molecule and a vibrational transition in the host molecules. This coupling manifests itself via a satellite of the I2(D′ → A′) band, which is shifted to the red by one quantum energy of the strongest IR-active vibrational mode of the CF4 (SF6) molecule. The lifetime of I2(D′) in studied molecular hosts varies from 2.5 ns in CF4 to 13 ns in SF6 solid.

Characterization of the potential minimum of the F ′u +(1D2) ion-pair state of Cl2 using (1 + 2′) optical-optical double resonance excitation and mass-resolved ion detection

Vibrational levels of the F(')0(u)(+)((1)D(2)), F0(u)(+)((3)P(0)), and D0(u)(+)((3)P(2)) ion-pair states of (35)Cl(2) and (35)Cl(37)Cl in the range 62,500-67,600 cm(-1) have been observed using (1 + 2(')) optical-optical double resonance excitation with mass-resolved ion detection. The strong F(')0(u)(+)((1)D(2))/F0(u)(+)((3)P(0)) coupling has been modelled by a coupled two-state calculation. An optimized fit of the experimental data used an F(')0(u)(+)((1)D(2)) state potential with a T(e) of 65,177 cm(-1) and an R(e) of ≈2.636 Å with a coupling constant of ≈430 cm(-1). The calculation assigns the first observed members of the F(')0(u)(+)((1)D(2)) state progression of (35)Cl(2) and (35)Cl(37)Cl at 64,998 and 65,094 cm(-1), respectively, as transitions to v = 0.

Dynamics and mechanism of the E→D, D′, β, γ, and δ nonadiabatic transitions induced in molecular iodine by collisions with CF4 and SF6 molecules

Nonadiabatic transitions among the first-tier ion-pair states of the iodine molecule in collisions with CF(4) and SF(6) partners are investigated by detecting the luminescence following the optical-optical double resonance excitation of the E0(g) (+)-state to the vibrational levels v(E)=8, 13, and 19. Total and partial rate constants, as well as vibrational product state distributions, are determined. It is found that electronic energy transfer in all channels is predominantly assisted by excitation of the dipole-allowed nu(3) and nu(4) modes of the partner. The measurements are accompanied by quantum scattering calculations that implement a close coupling treatment for the electronic and vibrational degrees of freedom and combine diatomics-in-molecule and long-range models for diabatic potential energy surfaces and coupling matrix elements. The analysis of experimental and theoretical data shows that the transitions without excitation of the partner are due to short-range couplings, whereas the vibrational excitation of the partner in the D0(u) (+) channel originates from the long-range coupling of two transition dipole moments: electronic of the iodine molecule and vibrational of the partner. Unexpectedly efficient excitations of the partner in the other ion-pair states, which are not coupled to the initial E0(g) (+)-state by the transition dipole, are interpreted within the postcollision mechanism. Qualitatively, this implies that during a single collision the long-range nonadiabatic transitions to D, nu(3) and D, nu(4) channels are followed by secondary short-range transitions without changing the state of the partner.

Isotope effects and Born-Oppenheimer breakdown in excited singlet states of the lithium dimer.

Observation of infrared electronic transitions involving the 1 (1)Deltag state of 7Li2 has instigated an investigation of Born-Oppenheimer breakdown in four singlet electronic states correlating with (2s+2s), (2s+2p), and (2p+2p) lithium atoms. The 1 (1)Deltag state, which correlates at long range with (2p+2p) atoms, has been observed in emission from the (5p) (1)Piu Rydberg state and in 1 (1)Deltag-B (1)Piu bands, in both instances following optical-optical double-resonance excitation. The latter transition was observed previously for the lighter isotopomer, 6Li2 [C. Linton, F. Martin, P. Crozet, A. J. Ross, and R. Bacis, J. Mol. Spectrosc. 158, 445 (1993)]. By analyzing multiple-isotopomer data for several electronic systems simultaneously, we have determined the electronic isotope shifts and the leading vibrational and/or rotational Born-Oppenheimer breakdown terms for the X (1)Sigmag+, A (1)Sigmau+, B (1)Piu, and 1 (1)Deltag states of the lithium dimer. This paper also reports Fourier transform measurements of the B-X absorption spectra of 6Li2 and 7Li2, which were required to better define the bottom portion of the B (1)Piu state potential.

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Sub-Doppler optical-optical double-resonance excitation spectra of BaF were recorded using two single-mode cw dye lasers. In the 30 000-cm−1 region, the electronic states observed were E2Σ+ and F2Π. The latter had been previously assigned as the “F2Σ+” state by Fowler [Phys. Rev.59, 645–652 (1941)]. The (3, 0) and (4, 0) bands of the E2Σ+-B2Σ+ transition and the (1, 0) and (2, 0) bands of the F2Π-B2Σ+ transition were rotationally analyzed. The molecular constants suggest inferences about the dominant atomic orbital character of the Rydberg molecular orbitals responsible for the E2Σ+ and F2Π electronic states. A new electronic state, the E′ 2Π, is predicted. The molecular parameters obtained (in cm−1, 1σ uncertainty in parentheses) are

Single-photon laser driven four-wave mixing in NO

When the 5sσ S 2 Σ + ( v=0) state of NO molecules was populated through optical-optical double resonance excitation via the 3sσ A 2 Σ + ( v=0) state, the strong red light belonging to the E 2 Σ + –A 2 Σ + system was generated along the laser propagating direction with a narrow divergent angle. On the evidences of several experimental results, we concluded that the visible radiation was produced by the four-wave mixing process. The characteristics of this radiation were compared with those of amplified spontaneous emission. In addition, the coexistence of the four-wave mixing and amplified spontaneous emission processes upon the excitation of 4pσ M 2 Σ + ( v=0) state was briefly reported.

The nd1Δ g ( n=11-15) Rydberg States of K2 Studied by Optical-Optical Double Resonance Spectroscopy and Space Charge Limited Diode Ionization Detector

Five bound nd 1Δ g ( n = 11-15) electronic states have been investigated using optical-optical double resonance excitation followed by ionization detection using an ultrasensitive space charge limited diode, which detects ion signals (presumably K + 3 produced by associative ionization). The molecular constants and the Rydberg-Klein-Rees potential curves for these states have been generated. The dissociation energies, additional binding energies, and molecular constants due to the weakly bound Rydberg bonding δ g orbitals are discussed.

Optical-Optical Double-Resonance Excitation Spectra of the (6 d) 1Δ g and (7 d) 1Δ g Rydberg States in Na 2

The levels with ν ≤ 14, 27 ≤ J ≤ 57 in the (6 d) 1Δ g and (7 d) 1Δ g Rydberg states of Na 2 have been observed using optical-optical double resonance (OODR) fluorescence excitation spectroscopy. The intermediate levels in the B 1Π u state are identified by numerical calculations with the molecular constants for B 1Π u ← X 1Σ + g transitions and confirmed by the complementary A 1Σ + u ← X 1Σ + g polarization spectra. Absolute vibrational numberings of the (6 d) 1Δ g and (7 d) 1Δ g states are determined by comparing the observed OODR excitation intensities of transitions 1Δ g ← B 1Π u with that of the simulated Franck-Condon factors. The Dunham coefficients and the Rydberg-Klein-Rees (RKR) potential energy curves of the (6 d) 1Δ g and (7 d) 1Δ g states are reported.

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Sub-Doppler optical-optical double-resonance excitation spectra of BaF were recorded using two single-mode cw dye lasers. In the 30 000-cm−1 region, the electronic states observed were E2Σ+ and F2Π. The latter had been previously assigned as the “F2Σ+” state by Fowler [Phys. Rev.59, 645–652 (1941)]. The (3, 0) and (4, 0) bands of the E2Σ+-B2Σ+ transition and the (1, 0) and (2, 0) bands of the F2Π-B2Σ+ transition were rotationally analyzed. The molecular constants suggest inferences about the dominant atomic orbital character of the Rydberg molecular orbitals responsible for the E2Σ+ and F2Π electronic states. A new electronic state, the E′ 2Π, is predicted. The molecular parameters obtained (in cm−1, 1σ uncertainty in parentheses) are

Optical-Optical Double-Resonance Excitation Spectra of the (6d) 1 Π g , (7d) 1 Π g High-Lying Rydberg States in Na 2

Two 1Πg states of Na2 for v ≤ 13 have been observed by using optical-optical double resonance (OODR) fluorescence excitation spectroscopy. The intermediate levels in B1Πu state are identified by the numerical calculations with the molecular constants for B1Πu ← X1Σg+ transitions and confirmed by the complementary A1Σu+ ← X1Σg+ polarization spectra. Absolute vibrational numberings of the (6d)1Πg and (7d)1Πg states are determined by comparing the experimental OODR excitation intensities with the simulated Franck-Condon factors. The Dunham coefficients and the Rydberg-Klein-Rees (RKR) potential energy curves of the (6d)1Πg, (7d)1Πg states are reported.

Optical-Optical Double-Resonance Excitation Spectra of the (8d)1Δg High-Lying Rydberg State in Na2

The levels with v from 1 to 9 in the (8d)1Δg state of Na2 have been observed by means of optical-optical double-resonance (OODR) fluorescence excitation spectroscopy. The intermediate levels in the B1Πu state are justified by numerical calculations with the molecular constants by Kusch and Hessel (J. Chem. Phys.68, 2591-2607 (1978)) for B1Πu ← X1Σ+g transitions and confirmed by the complementary experiments for polarization spectra of A1Σ+g ← X1Σ+g transitions. The Dunham coefficients and the Rydberg-Klein-Rees (RKR) potential energy curve of the (8d)1Δg state are determined.

The (2 p, 2 p) 1 1Δ g State of 6Li 2: Fourier Transform Spectrum of the 1 1Δ g- B1Π u Transition

The 1 1Δ g - B 1Π u transition of 6Li 2 has been observed in collisionally induced fluorescence following single frequency optical-optical double resonance excitation of the F 1Σ + g state using a ring dye laser with DCM dye. Spectra of the s and a symmetry levels were obtained separately, at high resolution, in the near-infrared region using a Fourier transform spectrometer. The molecular constants (Dunham coefficients) of the 1 1Δ g state have been calculated. Comparison of the constants and dissociation energy with ab initio calculations has shown that the 1 1Δ g state correlates with Li(2 p) + Li(2 p) and has a dissociation energy of 9579 ± 1 cm −1. The energy transfer process responsible for excitation of the 1 1Δ g state is discussed.

Parity Mixing in the Valence States of I2 Probed by Optical-Optical Double-Resonance Excitation of Ion-Pair: Characterization of a New Ion-Pair State, H1u(3P1), and a Valence State, c1g

Two new electronic states of molecular iodine are reported: the ion-pair H1u(3P1) state is characterized by its fluorescence excitation spectrum and dispersed fluorescence to the known a1g state, and a shallow bound valence state, the c1g state correlating with I(2P3/2) + I(2P1/2) is identified from the dispersed fluorescence spectrum, γIu → clg. Between 3.5 and 3.8 Å the independently derived H and c state potentials successfully reproduce the observed H (v′ = 0) → c dispersed fluorescence. The two ungerade ion-pair states H and γ are populated using the optical-optical double-resonance technique through a hyperfine coupled intermediate [BO+u (v = 59) ∼ clg (v = 14)]. The u/g coupling mechanism and the magnitude of the matrix element are deduced from the J-dependence of the mixing in the intermediate state, as monitored by the overall efficiency of two-photon production of an ungerade ion-pair state from the ground state.

Spectroscopy and multichannel quantum-defect theory analysis of the np Rydberg series of H3.

The lowest np Rydberg series of triatomic hydrogen has been studied using optical-optical double-resonance excitation from the metastable 2p2 A2\ensuremath{''} level. Bound states, detected by field ionization as well as autoionizing states of the p series are characterized using rotational multichannel quantum-defect theory. Deviations from the calculations appear when vibrational interactions give rise to predissociation below threshold or autoionizing interlopers above threshold. The np Rydberg manifold of H3 provides an almost complete panorama of channel interactions in a polyatomic molecule: rotational and vibrational interactions and autoionization with rich Fano profile structure as well as predissociation.

Determination of the radiative lifetimes of nine ion-pair states of I 2

The radiative lifetimes of 9 out of the 20 possible ion-pair states of I 2 have been measured using two-colour optical-optical double-resonance excitation. A pulse-shortened dye laser was used to populate the final state. Lifetimes for all six states in the first cluster - δ(2 u), γ(1 u), D(0 u +), D′(2 g) β(1 g) and E(0 g +) - have been measured again in view of the often d literature values. The lifetimes of three states in the second ion-pair cluster (H(1 u), F(0 u +) and f(0 g +)) are reported for the fir time. No significant pressure dependence was found up to 100 m Torr, with the exception of the longest lived γ state.

Optical-optical double resonance spectrum of Na 2: Observation of atomic and molecular ultraviolet emission

We have observed both atomic and molecular ultraviolet fluorescence following optical-optical double-resonance excitation in Na 2. The atomic fluorescence has been assigned as 4p-3s emission at 330 nm. Four possible excitation schemes are considered to account for these observations. All involve the near-degenerate (6) 1Σ g + and (5) 1Σ u + potentials of Na 2, which correlate to the atomic 3s+5s configuration and possess interesting double minima at very long range. The experimental and theoretical evidence points strongly to a route via the long-lived (2) 1Σ g + state.

An analysis of the F(O u+) ion-pair state of I 2 by optical-optical double resonance

An optical-optical double resonance (OODR) technique has been applied to study the spectroscopic details of the F(0 u +) ion-pair state of I 2 which correlates with I −( 1S) + I +( 3P 0) at the dissociation limit. In the excitation scheme, F(0 u +)- B 3Π(0 u +)- X 1Σ g +, the OODR excitation spectra show the vibrational progressions consisting of O, Q, and S branches in accordance with the selection rule (Δ J = 0, ±2) of the F(0 u +)- B 3Π(0 u +) two-photon transition. The F(0 u +)- X 1Σ g + fluorescence is resolved to establish the absolute vibrational numbering of the F(0 u +) state. Dunham parameters of the F(0 u +) state, based on a global least-squares fit analysis of 1184 transitions ( v′ = 0–48, J′ = 6–107), are reported. The main parameters, T e = 47 217.350 cm −1, ω e = 96.313 cm −1, and r e = 3.596 A ̊ , are consistent with the results derived from the vibrational analyses of the F(0 u +)- X 1Σ g + emission in the discharge. Our detailed analysis indicates some evidence that the lower vibrational levels of the F(0 u +) state are perturbed by an ion-pair state.

An analysis of the F′(0 u+) ion-pair state of I 2 by optical-optical double resonance

An optical-optical double resonance technique utilizing a stepwise three-photon transition has been applied to study the F′(0 u +) ion-pair state of I 2 which correlates with I −( 1S) + I +( 1D) at the dissociation limit. Two pulsed tunable dye lasers are used to excite the molecules to appropriate levels of the B 3Π(0 u +) state, and subsequently into the F′(0 u +) state by a simultaneous two-photon transition. The optical-optical double resonance excitation spectra show vibrational progressions consisting of O, Q, and S branches in accordance with the selection rule (Δ J = 0, ±2) of the F′(0 u +)- B 3Π(0 u +) two-photon transition. The absolute vibrational numbering of the F′(0 u +) state is established by the direct observation of the F′(0 u +)- X 1Σ g + fluorescence interpreted using the Franck-Condon factor calculations. Dunham parameters of the F′(0 u +) state, based on a global least-squares fit analysis of 1361 transitions ( v′ = 0–38, J′ = 6–108), are Y 00 = 51706.237(2), Y 10 = 131.00041(83), Y 20 = −0.516270(143) Y 30 = 4.2640(104) X 10 −3, Y 40 = −4.5797(330) X 10 −5, Y 50 = 2.8381(376) X 10 −7 Y 01 = 0.02194899(46), Y 11 = −9.2508(99) X 10 −5, Y 21 = 8.359(79) X 10 −7 Y 31 = −8.550(167) X 10 −9, andY 02 = −2.632(37) X 10 −9 (all in cm −1 with 1 SD in parentheses).