Optical-optical Double Resonance Technique Research Articles

Experimental study of the 61Σg+ state of the rubidium dimer

This paper reports a high-resolution experimental study and a numerical analysis of the ${\mathrm{Rb}}_{2}\phantom{\rule{4pt}{0ex}}{6}^{1}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ ion-pair state. A large number of rovibrational term values spanning a wide range of the rotational and vibrational quantum numbers were measured using the optical-optical double-resonance technique. The set of term values was simulated with a model of a piecewise multiparameter potential-energy function based on the generalized splines. This function reproduces the experimental data with reasonable accuracy and, in addition, allows us to incorporate in the potential function the nontrivial features at longer internuclear range, such as multiple wells, predicted by the ab initio calculations.

The Rb2 31Π g state: Observation and analysis.

This paper reports observations and analysis of the Rb2 31Π g state. A total of 323 rovibrational term values spanning the range of the rotational quantum number J = 7 through 77 and the vibrational quantum number = 2 through 23 (about 1/3 of the potential well depth) were measured using the optical-optical double resonance technique. The term values are simulated within a model of a piece-wise multi-parameter potential energy function based on the generalized splines. This function not only enables a reproduction of the experimental data with a reasonable quality but also approximates the available ab initio function in its whole range with a uniform accuracy.

The RgI2 (ion-pair states) van der Waals complexes

This paper is an overview of our recent experimental investigations of the RgI2 van der Waals complexes, Rg = He, Ar, Kr, performed by means of laser induced fluorescence spectroscopy, optical-optical double resonance and supersonic molecular beam techniques. Spectroscopic parameters of these complexes in the E0 g + ion-pair state, such as binding energies and several spectroscopic constants, have been determined. Most likely, the potential energy surfaces of the all RgI2(E) complexes under study present T-shaped minima. Vibrational and electronic predissociations of the RgI2(E) complexes were analyzed. Relative contributions of the different electronic predissociation channels and vibrational distributions of the decay products were determined. Possible mechanisms of the complexes decay are suggested and discussed.

Infrared radiative decay dynamics from the γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2) ion-pair states of I2 observed by a perturbation facilitated optical-optical double resonance technique.

We report the spectroscopic and temporal analyses on the amplified spontaneous emission (ASE) from the single rovibrational levels of the Ω = 1u ion-pair series, γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2), of I2 by using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg ∼ B (3)Π(0u (+)) hyperfine mixed valence state as the intermediate state. The ASE detected in the infrared region was assigned to the parallel transitions from the Ω = 1u ion-pair states down to the nearby Ω = 1g ion-pair states. The subsequent ultraviolet (UV) fluorescence from the Ω = 1g states was also observed and the relative vibrational populations in the Ω = 1g states were derived through the Franck-Condon simulation of the intensity pattern of the vibrational progression. In the temporal profiles of the UV fluorescence, an obvious delay in the onset of the fluorescence was recognized after the excitation laser pulse. These results revealed that ASE is a dominant energy relaxation process between the Ω = 1u and 1g ion-pair states of I2. Finally, the lifetimes of the relevant ion-pair states were evaluated by temporal analyses of the UV fluorescence. The propensity was found which was the longer lifetime in the upper level of the ASE transitions tends to give intense ASE.

Collision induced state-to-state energy transfer dynamics between the 2u ((1)D2) and 2g ((1)D2) ion-pair states of I2.

We report the first observation of collision induced state-to-state energy transfer from the 2u ((1)D2) (v2u = 3-7) ion-pair state of I2 using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg∼ B (3)Π(0) hyperfine mixed double-faced valence state as the intermediate state. The excitation of the 2u ((1)D2) state yielded the weak UV fluorescence from the wide range of vibrational levels in the nearby 2g ((1)D2) state. The vibrational distribution in the 2g ((1)D2) state derived by the Franck-Condon simulation of the UV fluorescence showed that the population in the 2u ((1)D2) state transfers mostly to the 2g ((1)D2) vibronic levels which are located energetically above the laser-prepared level. The radiative lifetimes and the self-quenching rate constants were determined to be 21.3 ± 0.1 and 44.6 ± 0.8 ns, and (1.30 ± 0.01) × 10(-9) and (2.26 ± 0.17) × 10(-9) cm(3) molecule(-1) s(-1) for the 2u ((1)D2) (v2u = 3) and 2g ((1)D2) (v2g = 5) states, respectively. The rate constant for the 2u ((1)D2) - 2g ((1)D2) collision induced state-to-state energy transfer was also evaluated to be (1.89 ± 0.01), (3.07 ± 0.07), and (3.77 ± 0.05) × 10(-10) cm(3) molecule(-1) s(-1) for the v2u = 3, 5, and 7 levels, respectively. The very large self-quenching cross sections for the ion-pair states of I2 could be explained by the harpoon mechanism.

Implementation of Various Modalities of the Optical-Optical Double Resonance Techniques To Simplify the Interpretation of the Spectra of Highly Excited States of Nitric Oxide.

We combined various modalities of the optical-optical double resonance (OODR) photoionization technique to simplify the interpretation of crowded molecular spectra. To demonstrate the effectiveness of our method, we applied it to the 64000 to 65200 cm(-1) spectral region of the molecule NO, where exist the following electronic states: B (2)Π (v = 21), D (2)Σ(+) (v = 5), F (2)Δ (v = 1), L (2)Π (v = 3), and K (2)Π (v = 0). This spectral region is complicated because (1) several electronic states are close in energy, (2) some of the rotational energy patterns are irregular, and (3) the relative intensity of the different bands varies markedly. We implemented four modalities of the OODR experimental technique that involved the combined use of two or three lasers. The individual rotational levels up to N' = 20 of the A(2)Σ(+) (v = 0) state were pumped as intermediate states by one-photon excitation from appropriate rotational levels in the X(2)Π (v = 0) ground state. Some of the schemes implemented provided information about line positions and relative band intensities, whereas the ion-dip detection scheme provided insight into the fate of the population in the different states. The term values that we derived are in good agreement with the literature ones. We rotationally resolved the spectra for the K (2)Π (v = 0) and B (2)Π (v = 21) states up to N = 20, and for the D (2)Σ(+) (v = 5) and L (2)Π (v = 3) states up to N = 8 and 7, respectively. Strangely, only in the rotational levels between N = 6 and N = 20 were we able to observe the F (2)Δ state, which is mostly mixed with the B' (2)Δ (v = 4) state and usually notated as F (2)Δ (v = 1) → B' (2)Δ (v = 4). We obtained the rotational constants for the B (2)Π1/2 (v = 21), L (2)Π3/2 (v = 3), and K (2)Π1/2 (v = 0) states, which had not been previously reported.

Far-infrared amplified spontaneous emission and collisional energy transfer between the $E\;0_g^ +$Eg+ (3P2) and $D\;0_u^ +$Du+ (3P2) ion-pair states of I2

We report direct observation of far-infrared amplified spontaneous emission from the E 0(g)⁺ ((3)P2) (v(E) = 0 - 3) ion-pair state of I2 by using an optical-optical double resonance technique with the B (3)Πu (0(u)⁺) (v(B) = 19) valence state as the intermediate state. The directional far-infrared emission detected in the wavelength range from 19 to 28 μm was assigned to the vibronic transitions from the E 0(g)⁺ ((3)P2) ion-pair state to the D 0(u)⁺ ((3)P2) ion-pair state. The subsequent UV fluorescence from the D 0(u)⁺ ((3)P2) state was also observed, which consists not only from the vibrational levels populated by the amplified spontaneous emission but also from those populated by collisional energy transfer. Analyses of the vibrational distribution in the D 0(u)⁺ ((3)P2) state revealed that the population transfer through the amplified spontaneous emission was dominant under our experimental conditions.

Laser induced amplified spontaneous emission from the $f\;0_g^ +$fg+ (3P) ion-pair state of I2

Laser induced amplified spontaneous emission (ASE) from the f 0g (+) ((3)P0) (vf = 1-7) ion-pair state of I2 was directly observed using an optical-optical double resonance technique with the B 0u (+) (vB = 21) valence state as the intermediate state. The emission detected at ~1660 nm was assigned to transitions from the f 0g (+) state to the D 0u (+) ((3)P2) ion-pair state. The transitions observed in the dispersed IR emission spectra were found to be between vibrational levels having the same vibrational quantum numbers in both electronic states, vf = vD. This is due to the almost parallel nature of the potential energy functions of the f 0g (+) and D 0u (+) states, leading to almost unit values for the Franck-Condon factors for vf = vD. That the observed infrared emission is due to ASE is shown by the facts that it propagated in a limited range of solid angles, exhibited a clear threshold against the input-laser power, and had different polarization to that of laser induced fluorescence.

Laser-induced fluorescence studies of HfF+ produced by autoionization

Autoionization of Rydberg states of HfF, prepared using the optical-optical double resonance technique, holds promise to create HfF(+) in a particular Zeeman level of a rovibronic state for an electron electric dipole moment search. We characterize a vibronic band of Rydberg HfF at 54 cm(-1) above the lowest ionization threshold and directly probe the state of the ions formed from this vibronic band by performing laser-induced fluorescence on the ions. The Rydberg HfF molecules show a propensity to decay into only a few ion rotational states of a given parity and are found to preserve their orientation qualitatively upon autoionization. We show empirically that we can create 30% of the total ion yield in a particular ∣J(+), M(+)<linear span> state and present a simplified model describing autoionization from a given Rydberg state that assumes no angular dynamics.

Improvement of the spectra signal-to-noise ratio of caesium 6P3/2–8S1/2 transition and its application in laser frequency stabilization

The spectra of the 133Cs 6P3/2–8S1/2 transition have been demonstrated by using both the double resonance optical pumping (DROP) and the optical–optical double resonance (OODR) techniques. Compared with the OODR technique, the DROP spectra show a much better signal-to-noise ratio and narrow spectral linewidth. When the frequency of a 795 nm external-cavity diode laser is stabilized to the DROP spectrum of 133Cs 6P3/2 F′ = 5–8S1/2 F″ = 4 transition, the lowest square root of the Allan variance of 4.1 × 10−12 at an averaging time of 100 s was obtained.

Nonadiabatic coupling in the 3Π3 and 4Π3 states of NaK

The excited 3 (3)Pi and 4 (3)Pi electronic states of the NaK molecule exhibit an avoided crossing, leading to the anomalous behavior of many features of the rovibrational energy levels belonging to each state. A joint experimental and theoretical investigation of these states has been carried out. Experimental measurements of the vibrational, rotational, and hyperfine structure of numerous levels of the 3 (3)Pi state were recently obtained using the Doppler-free, perturbation-facilitated optical-optical double resonance technique. Additional measurements for the 4 (3)Pi state as well as bound-free emission spectra from selected 3 (3)Pi, 4 (3)Pi, and mixed 3 (3)Pi to approximately 4 (3)Pi rovibrational levels are reported here. A model is also presented for calculating the mixed rovibrational level energies of the coupled 3 (3)Pi-4 (3)Pi system, starting from a 2x2 diabatic electronic Hamiltonian. The 3 (3)Pi and 4 (3)Pi potential curves and the coupling between them are simultaneously adjusted to fit the observed rovibrational levels of both states. The energy levels of the potential curves determined by the fit are in excellent agreement with experiment. The nonadiabatic coupling is sufficiently strong to cause an overall shift of 2-3 cm(-1) for many rovibrational levels as well as somewhat larger shifts for certain pairs of 3 (3)Pi to approximately 4 (3)Pi levels that would otherwise be very close together.

First observation of the B̃A11 state of SiH2 and SiD2 radicals by optical-optical double resonance spectroscopy

The B1A1 state of SiH2 and SiD2 was observed by the optical-optical double resonance technique for the first time. The electronic band origin of the B state of SiD2 was determined to be 27 214.11 cm(-1). A very clear exclusive behavior depending on the even/odd value of the bending vibrational quantum number was observed in the spectra, representing a quasilinear behavior of the B state. The barrier height to linearity was estimated to be approximately 125 cm(-1) by the quasilinear analysis of the bending vibrational level structure of SiD2.

Experimental study of the NaK 3Π3 double minimum state

We have used the Doppler-free, perturbation-facilitated optical-optical double-resonance technique to investigate the vibrational, rotational, and hyperfine structure of the 3Π3 double minimum state of NaK. Since this electronic state arises from an avoided crossing with the nearby 4Π3 state, we observe striking patterns in the data that provide a sensitive probe of the electronic wave function in the various regions of the double well potential. A single-mode cw dye laser excites 2(A)Σ+1(vA,J)∼1(b)ΠΩ=03(vb,J) mixed singlet-triplet “window” levels from thermally populated rovibrational ground state levels, 1(X)Σ+1(vX,J±1). Further excitation by a single-mode cw Ti:sapphire laser selects various 3Π03(vΠ,JΠ) rovibrational levels, which are detected by observing direct 3Π03→1(a)Σ+3 fluorescence in the green spectral region. Using the inverse perturbation approximation method, we have determined a 3Π03 potential curve that reproduces the measured energies to ∼0.24cm−1. In addition, the hyperfine and spin–orbit constants, bF and Av, have been determined for each region of the potential curve.

The d 1Πg(v=1) Rydberg state of O2: Optical-optical double-resonance and Huggins-band ozone-photolysis, resonance-enhanced multiphoton-ionization studies with a b 1Σg+(v=0)-state platform

Resonance-enhanced multiphoton-ionization spectra are presented of the d 1Πg←←b 1Σg+(1,0) transition of O2, the b(v=0) state generated both by photolysis of O3 in the Huggins bands and also by direct excitation of single J levels in an optical-optical double-resonance (OODR) experiment. The ozone-photolysis-derived spectra reveal a preferential formation of b(v=0) fragments with high J, the rotational distributions exhibiting significant dependence on the photolysis wavelength. Rotational analyses of the OODR and ozone-photolysis-derived spectra indicate that the d(v=1) Rydberg state is multiply perturbed by successive vibrational levels of the II 1Πg valence state. The OODR technique allows the first full resolution of the low-J levels of d(v=1) and the high-J levels favored by the ozone-photolysis technique are reported here for the first time.

Experimental and Theoretical Study of State-Resolved Electronically Inelastic Collisions of Highly Rotationally Excited CN(A2Π) with Argon and Helium: The Role of Gateway Levels

A collaborative study of A → X electronic transitions from CN(A 2 Π,v=3,N=60-63) fine-structure A-doublet levels induced by collisions with argon and helium is presented. Experimental state-to-state rate constants were determined with an optical-optical double resonance technique. Specific levels of CN(A 2 Π,v=3,N=60-63) were prepared by excitation of the photolytically generated radical with a pulsed dye laser on various rotational lines in the A 2 Π-X 2 Σ + (3,0) band, and collisionally populated levels in the v A = 3 and the nearly isoenergetic v X = 7 vibronic manifolds were probed after a short delay by laser fluorescence excitation in the B-X (3,7) and B-A (3,3) bands. Final state distributions (relative state-to-state rate constants) are reported for CN(A)-Ar collisions; the rate constants for transitions induced by He were considerably smaller. Absolute total removal rate constants were also determined. A crossing of the A 2 Π v = 3 F 1 f rotational/fine-structure manifold with the X 2 Σ + v = 7 F 2 levels occurs at J = 62.5. The dependence of A → X rate constants and the total removal rate constants on the initial level demonstrates the importance of this gateway in facilitating collisions between these manifolds. The experimental CN(A)-Ar rate constants have been compared with theoretical rate constants computed in a quantum scattering treatment of the dynamics based on ab initio CN(A,X)-Ar potential energy surfaces. The small non-Born-Oppenheimer mixing of the A and X states in the isolated CN molecule was also included in the calculations. The computed total removal rates show an enhanced value for the perturbed N = 62 F,f initial level, in agreement with experiment, but the computed state-to-state rate constants do not agree well with the experimentally determined values.

Dissociation dynamics of I2(B)–Ar: Rotational population distributions of I2(B,v) fragments from the T-shaped and linear complexes

Optical-optical double resonance techniques have been used to examine the dissociation dynamics of I2(B)–Ar. Rotational population distributions were characterized for the I2(B,v) fragments. Vibrational predissociation of the T-shaped complex yielded fragments with smooth rotational distributions. The high-energy limits of the distributions were consistent with events that channeled almost all of the available energy into product rotation. These data indicate a dissociation energy for I2(B)–Ar of D0(C2v)=220 cm−1. Most initial states of the complex produced bimodal rotational population distributions, but a few gave Boltzmann-type product distributions. The dependence of the character of the distribution on the initially excited state suggests that predissociation is mediated by intramolecular vibrational energy redistribution. Dissociation of linear I2(B)–Ar yielded fragments with Boltzmann type rotational population distributions. Excitation of the complex within the bound regions of the B–X transition gave rotationally cold I2(B,v) fragments, consistent with direct dissociation from a near-linear geometry. Excitation above the B state dissociation limit produced I2(B,v) fragments via caged recombination. The rotational distributions of these fragments were cold, supporting earlier studies that attribute the one atom cage recombination to the linear isomer.

Electric dipole moment function of the 1(3P2)A 1 3 transition in ICl

The optical-optical double-resonance technique has been used for measurements of emission spectra from separate vibrational levels of the 1(3P2) state of ICl (v´ = 12 and 14) populated via the A 1 3 state. The electric dipole moment function of the A transition has been determined over the range of the internuclear distance of 0.29-0.39 nm by means of simulation of the emission spectra from the state.

State to state collision energy transfer in singlet states of Li 2

This Letter reports on state to state collision energy transfer in the A 1 Σ u + and G(2) 1 π g states of both 7Li 2 and 6Li 7Li dimers. The molecules were electronically excited by a single laser excitation or by using optical-optical double resonance (OODR) technique. Either a fluorescence or an ionization signal was monitored. A breakdown of the symmetric antisymmetric (s ⇎ a) rotational level selection rule was observed for collisional transitions in the A 1 Σ u + state of th nearly homonuclear 6Li 7Li molecule. However, no s ⇎ a radiative transition breakdown was detected when we attempted the X 1 Σ g + → A 1 Σ u + → C(1) 1 π g ungerade-ungerade electronic excitation. Propensities for rotational energy transfer in the G(2) 1 π g state are discussed.

Optical-Optical Double-Resonance Spectroscopy of Cl 2: Analyses of the 0 +u, 1 u, and 2 u( 3P2) Ion-Pair States

The optical-optical double-resonance spectroscopy is applied to study the ion-pair states of Cl 2 correlating to Cl −( 1 S) + Cl +( 3 P 2). In the (1 + 2) photoexcitation sequence, we gain access to the 0 + u( 3 P 2) and 1 u( 3 P 2) ion-pair states through the A 3Π(1 u) and B 3Π(0 + u) states as intermediates. These states are found to lie closely together and show strong heterogeneous coupling with each other. The transitions to the nearby 2 u( 3 P 2) state are first noticed as extra lines through the mixing with the 1 u( 3 P 2) state, and the observations are extended by the perturbation-facilitated optical-optical double-resonance technique. The energy levels of the 0 + u, 1 u, and 2 u( 3 P 2) states are analyzed in detail by including the heterogeneous interaction between these states. The electronic structures of the ion-pair states are discussed. These results allow us to map out the ion-pair states and to clear up the puzzle of previously observed states in the 7-eV region.

Rotational quantum number and vibronic symmetry of nitrogen dioxide excited with visible light in the region of 563-566 nm: optical-optical double resonance measurement and spin-orbit interaction between 2B2 and 2A2 vibronic states

An optical-optical double resonance (OODR) technique has been employed to determine the rotational quantum number and vibronic symmetry of NO 2 in the region of 563-566 nm. The first excitation step corresponds to the intermediate 2 B 2 ←X~ 2 A 1 (0,0,0) transition of a parallel type. The lowest rotational levels are identical with those of the 17 713.203-cm -1 vibronic band reported by Delon et al. from their jet-cooled LIF experiment [J. Chem. Phys. 1991, 95, 5701]