The millimeter/submillimeter-wave spectrum of the SiP radical (X 2 Π i ) has been recorded using direct absorption spectroscopy in the frequency range of 151–532 GHz. SiP was synthesized in an AC discharge from the reaction of SiH 4 and gas-phase phosphorus, in argon carrier gas. Both spin–orbit ladders were observed. Fifteen rotational transitions were measured originating in the Ω = 3/2 ladder, and twelve in the Ω = 1/2 substate, each exhibiting lambda doubling and, at lower frequencies, hyperfine interactions from the phosphorus nuclear spin of I = 1/2. The lambda-doublets in the Ω = 1/2 levels appeared to be perturbed at higher J, with the f component deviating from the predicted pattern, likely due to interactions with the nearby excited A 2 Σ + electronic state, where ΔE Π-Σ ∼ 430 cm −1 . The data were analyzed using a Hund’s case a β Hamiltonian and rotational, spin–orbit, lambda-doubling, and hyperfine parameters were determined. A 2 Π/ 2 Σ deperturbation analysis was also performed, considering spin–orbit, spin-electronic, and L-uncoupling interactions. Although SiP is clearly not a hydride, the deperturbed parameters derived suggest that the pure precession hypothesis may be useful in assessing the 2 Π/ 2 Σ interaction. Interpretation of the Fermi contact term, b F , the spin-dipolar constant, c, and the nuclear spin-orbital parameter, a, indicates that the orbital of the unpaired electron is chiefly p π in character. The bond length in the v = 0 level was found to be r 0 = 2.076 Å, suggestive of a double bond between the silicon and phosphorus atoms.
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Direct mapping of curve-crossing dynamics in IBr by attosecond transient absorption spectroscopy
The electronic character of photoexcited molecules can abruptly change at avoided crossings and conical intersections. Here, we report direct mapping of the coupled interplay between electrons and nuclei in a prototype molecule, iodine monobromide (IBr), by using attosecond transient absorption spectroscopy. A few-femtosecond visible pulse resonantly excites the B ( Π 3 0 + ) , Y(0 + ), and Z(0 + ) states of IBr, and the photodissociation dynamics are tracked with an attosecond extreme-ultraviolet pulse that simultaneously probes the I-4 d and Br-3 d core-level absorption edges. Direct comparison with quantum mechanical simulations unambiguously identifies the absorption features associated with adiabatic and diabatic channels at the B/Y avoided crossing and concurrent two-photon dissociation processes that involve the Y/Z avoided crossing. The results show clear evidence for rapid switching of valence-electronic character at the avoided crossing.
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- Award ID(s):
- 1660417
- NSF-PAR ID:
- 10158292
- Date Published:
- Journal Name:
- Science
- Volume:
- 365
- Issue:
- 6448
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 79 to 83
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/science.aax0076
