Title: Bond dissociation energy and electronic spectroscopy of Cr ⁺ (NH ₃ ) and its isotopomers

Abstract

The electronic spectra of Cr ⁺(NH ₃), Cr ⁺(ND ₃), and Cr ⁺( ¹⁵NH ₃) have been measured from 14 200 to 17 400 cm ^-1 using photodissociation spectroscopy. Transitions are predominantly observed from the ⁶A ₁ ground state, in which the Cr ⁺ has a 3$$d$$ ⁵ electronic configuration, to the $$|tilde{B}$$ ⁶E ($$Π$$) state (3$$d$$ ⁴4s). There is extensive vibronic structure in the spectrum due to a long progression in the Cr–N stretch and transitions to all six spin-orbit levels in the upper state. The spin-orbit splitting in the excited state is observed to be A _so$$'$$ = 39 cm ^-1. For the lowest spin-orbit level, the Cr–N stretching frequency in the excited state is 343 cm ^-1, with an anharmonicity of 4.2 cm ^-1. The ⁶E ($$Π$$) origin is predicted to lie at T ₀ = 14 697 cm ^-1. The first peak observed is due to v$$'$$ = 1, so the observed photodissociation onset is thermodynamic rather than spectroscopic, giving D ₀(Cr ⁺-NH ₃) = 14 830 ± 100 cm ^-1 (177.4 ± 1.2 kJ/mol) and D ₀(Cr ₊–ND ₃) = 15 040 ± 30 cm ^-1 (179.9 ± 0.4 kJ/mol). The ⁶E ($$Π$$) state ofmore » Cr ⁺(NH ₃) is ~2740 cm ^-1 less strongly bound than the ground state, and the Cr–N bond length increases by 0.23 ± 0.03 Å upon electronic excitation. Calculations at the time-dependent density functional theory (M06) and equations of motion coupled cluster, with single and double excitations (EOM-CCSD) level fairly accurately predict the energy and vibrational frequency of the excited state. Multi-reference configuration interaction calculations show how the spin-orbit states of Cr ⁺(NH ₃) evolve into those of Cr ⁺ + NH ₃.« less

Authors:

Ashraf, Muhammad Affawn ^[1]; Kozubal, Justine ^[1]; Metz, Ricardo B.  ^[1]

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+ Show Author Affiliations

1. Univ. of Massachusetts, Amherst, MA (United States). Dept. of Chemistry

Publication Date:

2018-11-01

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Univ. of California, Oakland, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1543888

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 149; Journal Issue: 17; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Chemistry; Physics