A. M. Lyyra

Reactive collision dynamics by far wing laser scattering: Mg+H2

We have measured the far wing absorption profiles of the MgH2 collision system leading to both the nonreactive formation of Mg* and into two distinct final rotational states of the reaction product MgH (v‘=0, J‘=6, 23). We have observed qualitatively expected behavior including a pronounced red wing in the reactive absorption profile indicating strong reaction probability on the excited attractive potential surfaces. We have also observed novel aspects of the excited state dynamics including reactive vs nonreactive channel competition effects and a strong far blue wing reactive absorption suggesting significant reaction probability even for trajectories on the repulsive surfaces. We have developed a simple theoretical model to semiquantitatively explain our experimental results. This model uses standard quasistatic theory to estimate the absorption probability as a function of detuning between levels of MgH2 and with assumed nonreactive vs reactive branching ratios, accounts for the subsequent evolution on the excited potential surfaces. This theory correctly predicts the overall shapes of the profiles and in general gives reasonable predictions for the relative magnitudes of the wing intensities.We have measured the far wing absorption profiles of the MgH2 collision system leading to both the nonreactive formation of Mg* and into two distinct final rotational states of the reaction product MgH (v‘=0, J‘=6, 23). We have observed qualitatively expected behavior including a pronounced red wing in the reactive absorption profile indicating strong reaction probability on the excited attractive potential surfaces. We have also observed novel aspects of the excited state dynamics including reactive vs nonreactive channel competition effects and a strong far blue wing reactive absorption suggesting significant reaction probability even for trajectories on the repulsive surfaces. We have developed a simple theoretical model to semiquantitatively explain our experimental results. This model uses standard quasistatic theory to estimate the absorption probability as a function of detuning between levels of MgH2 and with assumed nonreactive vs reactive branching ratios, accounts for the subsequent evolution o...

Observation of the 39K2 a 3Σ+u state by perturbation facilitated optical–optical double resonance resolved fluorescence spectroscopy

Rydberg states of the potassium dimer in the 28 430–29 080 cm−1 and 30 030–30 500 cm−1 regions above the ground state X1Σ+g minimum have been studied using the perturbation facilitated optical–optical double resonance technique (PFOODR). Energy levels in these energy regions have been assigned to both triplet and singlet gerade states based on excitation pattern information as well as intensity considerations. Resolved fluorescence from a mixed triplet–singlet 43Πg ∼1Πg upper state to the ground triplet state a 3Σ+u has been used to construct a potential energy curve for the a 3Σ+u state which is in excellent agreement with recent theoretical results. Since this electronic state and the ground singlet state X1Σ+g share the same dissociation limit, we have determined the dissociation energy for the potassium dimer to be De=4450±2 cm−1.

CW all-optical triple-resonance spectroscopy of K2: Deperturbation analysis of the A1Σu+ (v ≤ 12) and b3Πu (13 ≤ v ≤ 24) states

Abstract The lowest vibrational levels v = 0 to 12 of the A1Σu+ state of K2, which are perturbed by the b3Πu state (13 ≤ v ≤ 24), were reexamined using all-optical triple-resonance (AOTR) spectroscopy. The experimental data were fitted by a nonlinear least-squares fit program to obtain deperturbed molecular constants for both the A1Σu+ and b3Πu states. Improved Dunham coefficients of the A1Σu+ state in the range 0 ≤ v ≤ 62 are determined from the deperturbed Tv and Bv values including the v ≤ 12 region of this work, the v = 12–18 region in the work of Ross et al. [J. Phys. B.20, 6225–6231 (1987)], and the v = 21–62 region in the work of Lyyra et al. [J. Chem. Phys.92, 43–50 (1990)]. The electronic matrix element for the A1Σu+ ∼ b3Πu interaction is Hel = 18.64(9) cm−1, in good agreement with the value of 18.4 (2) cm−1 found by Ross et al.

Hyperfine splitting of the 1 3Δg Rydberg state of 7Li2

The hyperfine structure of the 1 3Δg Rydberg state of Na2 has been studied by sub‐Doppler CW perturbation facilitated optical–optical double resonance (PFOODR) spectroscopy via A 1Σu+∼b 3Πu mixed intermediate levels.

The doubly excited 1 3Σ−g state of 7Li2

This paper reports the first experimental observation of the doubly excited valence (2p+2p)3Σ−g state of 7Li2. We used cw perturbation‐facilitated optical–optical double resonance (PFOODR) fluorescence excitation and resolved fluorescence spectroscopic techniques. All the observed levels have been detected through perturbations by the 2 3Πg state. The deperturbed primary molecular constants of this 1 3Σ−g state are Te=34 045.354(43) cm−1, ωe=216.820(37) cm−1, Be=0.673 69(47) cm−1, Re=2.670 81(94) A, and De=4279.306(43) cm−1. The equilibrium internuclear distance of the 1 3Σ−g state is smaller than that of the X 1Σ+g ground state.

New measurements of the a3 Σ+u state of K2 and improved analysis of long‐range dispersion and exchange interactions between two K atoms

Resolved fluorescence from the K2 43 Σ+g state to the a3 Σ+u state has been measured by the perturbation‐facilitated optical–optical double resonance (PFOODR) technique. Data have been fit to an improved set of molecular constants for the a3 Σ+u state. In particular, the new Te value for this state has been determined as 4197.935±0.047 cm−1, nearly 1.8 cm−1 higher than previously reported. By combining the new results for the a3 Σ+u state and the recent results for the ground X1 Σ+g state [J. Chem. Phys. 103, 3350 (1995)], we report in this paper an improved analysis of long‐range dispersion and exchange interactions between two K atoms and of the X1 Σ+g and a3 Σ+u state dissociation energies De of 4450.674±0.072 cm−1 and 252.74±0.12 cm−1, respectively.

Perturbation facilitated optical–optical double resonance spectroscopy of the 2 3Σ+g, 3 3Σ+g, and 4 3Σ+g Rydberg states of 7Li2

This paper reports the experimental observation of the 2 3Σ+g, 3 3Σ+g, and 4 3Σ+g states of 7Li2 by cw perturbation facilitated optical–optical double resonance spectroscopy. Molecular constants and RKR potential curves have been obtained. Our experimental Te and Re for the 2 3Σ+g state are 27 297.45(16) cm−1 and 3.0797(18) A, respectively, and for the 3 3Σ+g state are 31 043.93(53) cm−1 and 3.0378(19) A, respectively. The above values are in very good agreement with theoretical calculations. Hyperfine splitting for both states has been resolved. Both states follow Hund’s case (bβS) hyperfine coupling scheme. The experimental Fermi contact parameter, bF, is approximately 96±2 MHz for the 2 3Σ+g state and 95.6±3 MHz for the 3 3Σ+g state. These values are in good agreement with the previously obtained value 98.6±4 MHz [Li et al., J. Chem. Phys. 96, 3342 (1992)]. One level of the 4 3Σ+g state has been observed and its hyperfine structure has been resolved and characterized with Hund’s coupling case (bβS).

Hyperfine structures of the 7Li2 b3Πu, 23Πg, and 33Πg states: Continuous wave perturbation facilitated optical–optical double resonance spectroscopy

The hyperfine structure of the b 3Πu, 2 3Πg, and 3 3Πg states of 7Li2 has been studied by continuous wave perturbation facilitated optical–optical double resonance fluorescence excitation spectroscopy. The b 3Πu state has case bβJ coupling scheme. The hyperfine splittings of the two perturbed b 3Πu v=19, N=10, J=11e, s, F1 and v=19, N=5, J=4e, a, F3 levels were resolved and hyperfine constants determined to be +9.90 MHz and −20.94 MHz, respectively. Fermi contact is the main source of the hyperfine interaction and bF(b 3Πu)=+107 MHz has been obtained. The coupling schemes of different 2 3Πg levels are different: N=4, 6 levels observed from the b 3Πu v′=19, N′=5, J′=4e, a, F3 intermediate level and the N=10 levels observed via the b 3Πu v′=19, N′=10, J′=11e, s, F1 intermediate level have case bβJ coupling; the N=5 levels observed via the b 3Πu v′=19, N′=5, J′=4e, a, F3 intermediate level and the N=9, 11 levels observed from the b 3Πu v′=19, N′=10, J′=11e, s, F1 intermediate level are closer to case bβS cou...

All optical triple resonance spectroscopy of the A 1Σ+u state of 7Li2

The A 1Σ+u state of 7Li2 has been studied using all optical triple resonance spectroscopy. Vibrational levels v=27–62 and rotational levels ranging from J=0 to 27 have been observed. This represents a region between previous data from single photon experiments and new data from cold atom photoassociative spectroscopy. Our data was fit to a Dunham expansion and the resulting molecular constants reproduce most observed energies to within 0.050 cm−1. A Rydberg–Klein–Rees potential curve has also been constructed and the calculated eigenvalues are in good agreement with observed energies.

Spin–orbit interactions, new spectral data, and deperturbation of the coupled b 3∏u and A 1∑u+ states of K2

We report calculations of the spin–orbit energy as a function of internuclear distance R within the b 3∏u state of K2, and between the b 3∏0u and A 1∑u+ states, together with new spectroscopic data on the b state and previously unpublished data on the A state. Both the new data and previous data are fitted to Hamiltonian parameters using the discrete variable representation (DVR) method. The DVR matrix includes nonrelativistic Born–Oppenheimer potentials and spin–orbit interactions, which are scaled to match the known asymptotic limits and to best fit the experimental data. We report fitted Dunham coefficients that yield the A and b state potentials by means of the Rydberg–Klein–Rees method. These parameters thus take into account second-order spin–orbit perturbation shifts (from the vibrational levels of these two states) which are normally not considered in band-by-band fits to spectroscopic data.