Rotational state distributions from vibrational autoionization of H₂

Journal Article · Sun Jan 01 00:00:00 EST 1989 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.456341· OSTI ID:6068335

Dehmer, Joseph L. ^[1]; Dehmer, Patricia M. ^[1]; Pratt, Stephen T. ^[1]; Tomkins, F. S. ^[1]; O’Halloran, M. A. ^[2]

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1. Argonne National Lab. (ANL), Argonne, IL (United States)
2. Univ. of Oklahoma, Norman, OK (United States)

Optical--optical double-resonance excitation together with electron spectroscopy was used to measure the H⁺₂ rotational state distributions produced by vibrational autoionization of singlet n p Rydberg states of H₂ . In the two-color excitation scheme, one laser was used to excite the two-photon transition to the H₂ E, F ¹Σ⁺_g, v'=1, J'=1 state, and a second laser was used to probe single-photon transitions to the vibrationally autoionized n p Rydberg series converging to the X ²Σ⁺_g, v⁺=1, N¯⁺=1 and N¯⁺= 3 levels of the ion. The expected P(1)n pσ, Q(1)n pπ, R(1)n p1, and R(1)n p3 Rydberg series converging to v⁺=1 were observed and assigned, as were several interlopers converging to higher vibrational levels of the ion. Rotationally resolved photoelectron spectra were determined for all of the autoionizing transitions by using a magnetic bottle electron spectrometer. Under the normal assumptions that p waves are ejected and that spin effects are negligible, vibrational autoionization of the upper levels of the P(1)n pσ and Q(1)n pπ transitions should produce only v⁺=0, N⁻⁺=1, while vibrational autoionization of the upper levels of the R(1)np1 and R(1)n p3 transitions should produce a mixture of v⁺=0, N¯⁺= 1 and v⁺=0, N¯⁺=3. Significant deviations from these expectations were observed. For example, vibrational autoionization of the upper levels of the Q(1)n pπ transitions produced substantial amounts of v⁺=0, N¯⁺=3, while vibrational autoionization of the upper levels of certain Q(1)n pπ, R(1)n p1, and interloper transitions produced nonnegligible amounts of v⁺=0, N¯⁺=5. This indicates that vibrational autoionization of n pπ Rydberg states is accompanied by rotational state changes in the H⁺₂ core to an unexpected degree, and that additional mechanisms for exchange of angular momentum within the excited complex must be considered. Possible contributing mechanisms are critically assessed.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE; Office of Health and Environmental Research (OHER)
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 6068335
• Journal Information: Journal of Chemical Physics, Vol. 90, Issue 11; ISSN 0021-9606
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
HYDROGEN
AUTOIONIZATION
ENERGY-LEVEL DENSITY
DISTRIBUTION
ELECTRON SPECTROSCOPY
ENERGY TRANSFER
LASER RADIATION
MULTI-PHOTON PROCESSES
ROTATIONAL STATES
RYDBERG STATES
VIBRATIONAL STATES
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY LEVELS
EXCITED STATES
IONIZATION
NONMETALS
RADIATIONS
SPECTROSCOPY
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory