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Discusses the application of an infrared spectroscopic technique for jet-cooled molecular cations to observe intramolecular hydrogen bonds in substituted phenol ions. Measurement of vibrational transitions of an ion core of high Rydberg states by detecting molecular ions prepared through vibrational autoionization.

In a series of spectroscopic work of the Rydberg states of CO, we present the rotational analysis of the v=0 and 1 levels of the singlet ns, np, nd and nf-Rydberg states (n=4–7). The spectra were measured by ion-dip spectroscopy with triple resonance excitation via the 3sσ:B 1Σ+ or the 3pσ:C 1Σ+ state. All the spectra were rotationally well resolved and the term value, quantum defect and the rotational constant were obtained for each state. Through the analysis of the rotational structure, the coupling between the Rydberg electron and the ion core has been investigated. For the np-Rydberg states, a switching from Hund’s case (b) to (d) was clearly observed with the increase of n. A significant perturbation was observed in the 6pπ 1Π and 7pπ 1Π states and it is suggested that these states are perturbed by the state with the same symmetry. For the nf-Rydberg states, the observed electronic energy was well analyzed by the long range force model and the precise ionization potential was obtained. The Rydbergvalence and inter-Rydberg states interactions were also investigated. For the ns-Rydberg states, the interaction matrix element with the repulsive state was estimated from the measurement of linewidth of the rotational levels. The potential curve of the repulsive state to which ns-Rydberg states predissociate was also determined. Selective predissociation was found for the e-symmetry levels both in the v=0 and 1 levels of the nf-Rydberg state. A strong interaction between the v=0 levels of the 6d- and 7s-Rydberg states was observed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rotationally resolved spectra of the 5s–7s, 5p–7p, 5d, 6d, and 4f–6f Rydberg states (v=1) of jet cooled CO have been measured by ion-dip spectroscopy with triple resonance excitation via the 3sσ B 1Σ+(v=1) state. The dip spectra due to the high Rydberg (v=1)←B 1Σ+(v=1) transition revealed the states most of which have not been observed by other spectroscopy. By the rotational analysis of the dip spectra, electronic term values, quantum defects, and rotational constants were obtained. For the np Rydberg states, the change of the angular momentum coupling between the p Rydberg electron and the CO+ core was clearly observed as a function of the principal quantum number, n, indicating a transition from Hund’s case (b) to Hund’s case (d). It was found that the rotational constant of the nsσ state increases with n, while that of the ndσ state decreases. The changes in the rotational constants were interpreted by the mixing between the nsσ state and the (n-1)dσ state and the mixing coefficients for those states were determined. For the 4f, 5f, and 6f Rydberg states, only the rotational levels belonging to e-symmetry were observed in the dip spectrum. It indicates the selective predissociation through the low lying D’ 1Σ+ state. [ABSTRACT FROM AUTHOR]

A detailed analysis of the rotational structure of high Rydberg states of CO converging to the ionic state is presented. These states were pumped from the 3sσB 1Σ+ state using triple resonant multiphoton excitation. The observed states were n=8∼10 of the s-, p-, d-, and f-Rydberg states in the vibrational levels with v=1. The observed spectra were rotationally well resolved and the term values, the quantum defects, and the rotational constants were obtained for these states. p- and f-Rydberg states were described by the Hund’s coupling case (d). On the other hand, only the σ component was observed for the d-Rydberg states and its linewidth was very broad. For the nf-Rydberg state, the long range force model was used to obtain the ionization potential of CO(v=1), the polarizability and the quadrupole moment of the CO+ core. The mixing among Rydberg states seems to be large, as suggested by anomalous values of the rotational constants for several states. In particular, in the nf-Rydberg states, a rotational branch that should not appear for a pure Rydberg state was observed, and was explained by mixing with nearby (n+1)s-Rydberg states. [ABSTRACT FROM AUTHOR]

The two-color double resonance multiphoton ionization and fluorescence dip spectra due to the transitions from various rotational levels of the D 2Σ+ (v=1) state of NO to its high Rydberg states have been measured. Coherent vacuum ultraviolet (VUV) light generated by four wave mixing in Hg was used in the first excitation step. The ns(v=1) and nd(v=1) Rydberg series with 7≤n≤32 were observed. The rotational analysis for the d Rydberg series indicates that only the Π- component appears in the MPI spectra. A large dependence of the rotational constant upon n for the nd Π- Rydberg states was found and interpreted in terms of dΠ-–dΔ- mixing. An anomalous intensity distribution was also found for the rotational branches of the ns Rydberg states in the transition from the D 2Σ+ state. The anomaly is explained by the ns–(n-1)d mixing. [ABSTRACT FROM AUTHOR]

Examines the Rydberg states of carbon monoxide by monitoring the fragment atoms generated by predissociation. Measurement of the photofragment atoms produced by the predissociation process; Determination of the molecular constants of the Rydberg states; Comparison of predissociation rates between the triplet and singlet channel.

Predissociation of Rydberg states of CO has been investigated by the C ([sup 3]P and [sup 1]D) and O([sup 3]P) photofragment measurements in the region of 103 000-114 000 cm[sup -1] (88-97 nm). The simulations of the rotational structures of np and nf Rydberg states were also carried out by using the l-uncoupling Hamiltonian model. The photofragment yield spectra were compared with the ion-dip spectra which correspond to the absorption spectra, indicating that all the Rydberg states, ns, np, nd, and nf converging to the X [sup 2]Σ[sup +] CO[sup +] ion, were subject to the predissociation. It was found that the lower member npπ and ndπ states exhibit two dissociation path ways, that is the C([sup 3]P)+O([sup 3]P) and the C([sup 1]D)+O([sup 3]P) channels. Especially, for the 4pπ L [sup 1]Π(v=0) state the two channels were found to be competitive with respect to parity as well as rotational quantum number J. At higher np series, such a parity and J-dependence of the predissociation disappeared, and the observed rotational structure was simulated very well by the model with no parity nor J dependence. For the ndσ states, the spectra of the 3dσ and 5dσ(v=0) states were diffuse, while the 4dσ(v=0) state showed a rotationally resolved photofragment yield spectrum. All the photofragment yield spectra of the nf(v=0) states exhibited sharp structures compared with those of other Rydberg states with a small l value. From a comparison between the photofragment yield spectrum and the ion-dip spectrum, it was found that the predissociation rate of the e-symmetry component is larger than that of the f-symmetry component. It was suggested that the e-symmetry levels predissociate through D[sup ′] [sup 1]Σ[sup +] valence states, while the f-symmetry levels predissociate through the 2 [sup 1]Π state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]