Study of the B″B¯Σu+1 state of H2: Transition probabilities from the ground state, dissociative widths, and Fano parameters

Predissociation dynamics of D2 revealed by variation in fragment anisotropy parameters along the Fano profile

We conducted a study on the variations of the fragment anisotropy parameters (β) along the Fano profiles for the predissociation of the D2 molecule. These variations, known as β profiles, were measured for the D(2l) fragments from the predissociation of the 4pπD'Πu1υ'=1 and 4pσB″Σu+1υ'=2 states. The measured β profiles show significant asymmetry and broader linewidths compared to the corresponding Fano profiles. By fitting the β profiles, we were able to determine the fragment anisotropy parameters associated with the resonance state, continuum state, and the interference effect between them. Additionally, we determined the ratios of the absorption cross sections between the unperturbed and perturbed continuum states interacting with the resonance states although these ratios were found to be very small. Furthermore, we derived approximate formulas to calculate the parameters characterizing the β profile. Despite the linewidths of the four Fano profiles being narrower than our instrumental resolution, we were still able to determine the product of the linewidth with the Fano q parameters. These findings demonstrate the utility of the β profile as an effective tool for studying the predissociation dynamics in diatomic molecules.

Spectra and Predissociation Dynamics of the 4pσB''1∑u+ and 4pπD' 1Πu States of D2

The spectra and predissociation dynamics of the Rydberg states 4pσB″1∑u+(υ'=2) and 4pπD'1Πu±(υ'=1) of the D2 molecule have been studied by a combination of XUV laser pump, UV laser probe, and velocity map imaging methods. The D(2l) fragment yield spectrum and the D2 excitation spectrum have been measured. Although the predissociation rates were found to be small and comparable to the radiative decay rates, the D(2l) fragments were observed for all the Rydberg states. The measured D(2l) fragment angular distributions are in good agreement with a reported model that has an analytical formula for anisotropy parameters. The results demonstrated that the 4pσB″1∑u+ and 4pπD'1Π u+ states dissociate via direct and indirect coupling with an 1∑u+ state, respectively. For predissociation of the 4pσB″1∑u+ state, the experimental data showed that D(1s) + D(2s) is the main channel, supporting previous theoretical predictions that the predissociation occurs by coupling to the vibrational continuum of the 3pσB'1∑u+ state.

Predissociation dynamics in the 3pπD(1)Πu (±)υ=3 and 4pσB(″) (1)Σu (+)υ=1 states of H2 revealed by product branching ratios and fragment angular distributions

The predissociation dynamics of H2+XUV→H2 (*)→H(1s)+H(2s,2p) has been studied by measuring the fragment branching ratios between the H(2s) and H(2p) states and the fragment angular distributions using the XUV (extreme ultraviolet) laser pump and UV(ultraviolet) laser probe method. The fragment angular distributions for the predissociation of the 3pπD(1)Πu (+)υ=3 state show parallel transitions, demonstrating that the main components of the dissociating state have (1)Σu (+) symmetry. The measured fragment branching ratios, H(2s)/(H(2s) + H(2p)), for the transitions R(0), R(1), and P(2) in 3pπD(1)Πu (+)υ=3←X(1)Σg (+)υ(″)=0 are in good agreement with one of the previous theoretical predictions. The predissociations of the 3pπD(1)Πu (-)(υ=3) state arising from the Q(1), Q(2), and Q(3) lines have also been observed. The angular distributions and the state distributions of the excited fragments (all found from the H(2p) state) illustrate that the dissociating states for the Q lines have the expected Πu (-) symmetry. The predissociation dynamics of the transition 4pσB(″1)Σu (+)υ=1←X(1)Σg (+)υ(″)=0 was also studied. Their fragment angular distributions show the expected parallel transitions, and most of the fragments are in the H(2s) states. The Beutler-Fano profiles and the associated spectroscopic parameters for the predissociations have also been obtained by measuring the fragment yield of H(2s, 2p) as a function of excitation photon energies.

The J = 2 ortho levels of the v = 0 to 6 np singlet Rydberg series of molecular hydrogen revisited

The energies of the J = 2 ortho levels of the v = 0 to 6 Rydberg np singlet series of molecular hydrogen with absolute intensities of the R(1) and P(3) absorption lines were measured by a high-resolution synchrotron radiation experiment and calculated through a full ab initio multi-channel quantum defect approach.

The J = 1 para levels of the v = 0 to 6 np singlet Rydberg series of molecular hydrogen revisited

The energies and the widths of the J = 1 para levels of the v = 0 to 6 Rydberg np singlet series of molecular hydrogen with absolute intensities of the R(0) and P(2) absorption lines were measured by a high - resolution synchrotron radiation experiment and calculated through a full ab initio multichannel quantum defect theory approach. On the basis of the agreement between theory and experiment, 31 levels were either reassigned or assigned for the first time.

The transition probabilities from the ground state to the excited J = 0 1Σu(+) levels of H2: measurements and ab initio quantum defect study

The energies, widths and absolute intensities of the P(1) v'' = 0, J'' = 1 absorption transitions of H(2) have been measured in the spectral range of 81-75 nm using monochromatized synchrotron radiation. This work completes and extends previous observations, in particular those of Herzberg and Jungen [J. Mol. Spectrosc. 41, 425 (1972)]. Ab initio multichannel quantum defect theory (MQDT) is used to corroborate the spectral analysis of the experimental data. Line intensities and decay widths are also calculated using MQDT.

H2 superexcited states: experimental and theoretical characterization of their competing decay-channel fluorescence, dissociation, and ionization

The absolute cross sections for the competing decay channels fluorescence, dissociation, and ionization of photoexcited long-lived superexcited H(2) molecular levels have been measured from the ionization threshold of H(2) up to the H(1s)+H(n=3) dissociation limit. The total and partial natural widths of these levels have been determined. Good agreement is found with first principles calculations carried out by multichannel quantum defect theory. The calculations reproduce the balance between the competing decay processes as well as its substantial level-to-level evolution.

The study of the D(') (1)Pi(u) state of H(2): transition probabilities from the ground state, predissociation yields, and natural linewidths

The absorption spectrum of the H(2) molecule was studied at high resolution in the 81-72 nm spectral range. A detailed analysis of the D(') (1)Pi(u)-->X (1)Sigma(g) (+) electronic band system is reported. In the spectrum, more than 70 new lines were assigned. For wavelengths longer than 75 nm, the D(') (1)Pi(u) (+) and (1)Pi(u) (-) components show a clearly different behavior: Tauhe (1)Pi(u) (+) one dissociates into H(1s)+H(n=2) whereas the (1)Pi(u) (-) one leads to molecular fluorescence. For shorter wavelengths, both components are predissociated into H(1s)+H(n=3). The predissociation yields, the dissociation widths, and the absolute values of the transition probabilities were measured over the vibrational progression from v(')=3 to 17, i.e., up to the dissociation limit. The comparison between these absolute transition probabilities and the values calculated in the adiabatic and nonadiabatic approximations demonstrates clearly the importance of nonadiabatic couplings.