Angular distributions and separation energies of predissociation photofragments of O2+ (b 4Σg−, v′=4, N′, F′)

Abstract

Kinetic energy distributions have been measured for O+ photofragments resulting from transitions O2+ (a 4Πu, v″, J″, Ω″) →O2+ (b 3Σg−,v′=4,N′,F′) →O+(4S0) +O(3P), where for the first time in the study of photodissociation all relevant quantum numbers involved are specified. Both 16,16O2+ and 16,18O2+ were studied. The measurements were made using a laser-ion coaxial-beams photofragment spectrometer, a single-mode laser, and velocity tuning of the absorption wavelength. Experimental values of the anisotropy parameter β, which describes the angular distributions of the photofragments, were obtained by fitting the experimental energy distributions with calculated distributions, obtained from a Monte Carlo computer simulation of ion trajectories in the apparatus. Values of β were thus determined with an uncertainty of ±0.05 or less. They are compared with theoretical values of β obtained by a generalization to Hund’s case (b) of the theory previously developed by R. N. Zare. In a similar manner, values of the kinetic energy of separation of the photofragments in the center-of-mass system, W, are determined with an accuracy, in the most favorable case, of ±0.14 meV. The experimental W values are used, along with other spectroscopic data, to improve the bond dissociation energy values of the ground X 3Σg− state of O2, and of the a and b states of O2+. It is shown that for W<50 meV the dissociation strongly favors the O(3P2) channel over 3P1 and 3P0. This result is compared with several possible limiting-case models of the long-range couplings involved in the dissociation process, and it is concluded that the dissociation proceeds in a completely adiabatic way. Finally, further possible refinements of the present work are discussed.

Complete characterization of the 3p Rydberg complex of a molecular ion: MgAr+. I. Observation of the Mg(3pσ)Ar+ B+ state and determination of its structure and dynamics

“…The sum over M on the right-hand side of the above equation is known analytically and can be written as 1 2 (1 + β J J P 2 (cos θ)). The corresponding formulas for β J J have been tabulated by Zare 64 (see also Pernot et al 55 ).…”

“…Following a theoretical procedure similar to that introduced by Pernot et al 55 , the β parameter associated with the excitation from a given X + (v , N ) rovibrational level to a B + (v , J ) predissociative level can be expressed within second-order perturbation theory as (see Appendix B)…”

“…PLEASE CITE THIS ARTICLE AS DOI:10.1063/5.0015603 by Hund's coupling case (b), with a projection quantum number of the orbital angular momentum on the internuclear axis Λ , a spin angular momentum quantum number S , a total angular momentum quantum number without spin N , a total angular momentum quantum number J , and a set of other good quantum numbers i, to a predissociative state described by Hund's coupling case (c) with a total angular momentum quantum number J and its projection quantum number Ω onto the internuclear axis, and a set of other good quantum numbers e. The anisotropy parameters β J J associated with each J ← J transitions are known analytically (see, e.g., Ref. 55), and tend to values of 1 2 for J = J ± 1 (P and R branches) and −1 for J = J (Q branch) in the limit of large J values. The total β N J parameter is therefore the weighted sum of the β parameters of the transitions from the various J sublevels of a given N level, with weights given by the relative strengths of the different branches.…”

Accurate ab initio potential energy curve of O2. II. Core-valence correlations, relativistic contributions, and vibration-rotation spectrum

“…18,19 This makes the determination of the complete vibrational spectrum of the ͑ 3 ⌺ g − ͒ state a challenging task [22][23][24][25][26][27] and its higher vibrational levels were only rather recently reported. The experimental determination of D 0 ͑X͒ has been the focus of numerous studies [28][29][30][31][32] with numerical values ranging from 41 256.6 ͑Ref. 26 In spite of this considerable increase in the experimental information, the highest level v = 35 lies still about 1400 cm −1 below the separated atom limit while the spacing between levels 34 and 35 is 562 cm −1 , which suggests the existence of additional levels.…”

Asymmetry of the Polarized-Laser-Induced Photofragmentation of Oriented CH3I Molecules

“…For prompt, parallel dissociation 7 /?=2, as found 8 " 10 for CH3I; the promptness was verified by direct real-time, subpicosecond measurements. 11 By ionization of one of the photoproducts from dissociation, it is possible to measure the z components of its velocity, 12,13 in both the + z and the -z directions. Hence any measured ± z asymmetry in the intensity of the fragment is indicative of the degree of orientation of the parent molecule.…”