Magneto-Optical Investigations of Imidogen in Inert-Gas Matrices

Abstract

Magnetic circular dichroism (MCD) and absorption spectra are reported for the A 3 Π i r X 3 Σtransition of imidogen (NH) isolated in Kr, Xe, and N 2 matrices at cryogenic temperatures (∼1.4-20 K) and over a range of magnetic field strengths (0-5 T). The results are analyzed by the method of moments, and parameters are extracted by fitting the experimental data to a model in which the A 3 Π i term is split by spin-orbit (SO) coupling interactions and the X 3 Σterm is split by spin-spin and higher-order SO coupling. The analysis indicates that the ground-state NH radicals behave essentially as free rotors in the noble-gas matrices but as hindered rotors in solid N 2 . Trends in excited-state SO coupling constants are attributed to the external heavyatom effect.

Magnetic Circular Dichroism and Absorption Spectra of Phosphinidene in Noble-Gas Matrices

“…As noted above, rotational hindrance gives rise to a nonzero D′, which can, in principle, approach the gas-phase D value. Near-zero D′ values found for NH/NG (compared with D ) 1.67 cm -1 for gas-phase NH) 21 were, therefore, interpreted 1,2 as corroboration of conclusions by earlier workers using other techniques 3,4 that ground-state NH behaves as a free rotor in noble-gas matrices. In contrast, D′ ) 0.61 cm -1 for NH/N 2 2 is consistent with the expectation that guest rotations should be significantly hindered in nitrogen matrices.…”

“…These transitions are closely analogous to those with the same designation for NH, and their analysis is essentially the same as that which we have described earlier. 1,2 The most significant alteration is the omission of consideration of excited-state crystal-field effects. Although these will certainly be present for PH/NG, they do not affect the lower spectroscopic moments, 16 and the spectra do not exhibit sufficient structural detail to permit the more explicit modeling of band shapes that is required for their elucidation.…”

Magnetic Circular Dichroism and Absorption Spectra of Methylidyne in a Krypton Matrix

“…Second, the one-electron SO coupling constant, a π = A Π for the X 2 Π term of CH is shifted progressively negative from its gas-phase value of 31.8 cm –1 by incorporation of the radical into heavier noble gas matrices. This parallels trends for the one-electron SO coupling constants a π for the A 3 Π i term of NH and ζ p for 2 P terms of alkali metals − and lighter coinage metals. , It is consistent with the well-documented external heavy-atom effect in noble-gas matrices and (in simplistic terms) can be qualitatively rationalized by the fact that electronic orbital angular momentum in one sense about an internal nucleus (belonging to the guest) represents angular momentum in the opposite sense about external nuclei (of the host). The situation for the A 2 Δ term is different.…”

“…Over a period of more than a decade, we have used MCD and absorption spectroscopy to investigate monohydride radicals of group 14–16 elements isolated in noble-gas matrices (XH/NG) with the aim of characterizing guest–host interactions. − To interpret the data, we have used a spin-orbital plus crystal-field (SO–CF) model initially developed to explain the spectra of TiO/Ar . Recently, the XH/Ar experimental data have elicited interest as tests for quantum computational methods for calculating the MCD of open-shell molecules, , whereas the SO–CF model has been adapted by Ernst and coworkers to inform their interpretation of the MCD spectra of alkali molecules and potassium atoms on the surfaces of He nanodroplets.…”

Application of magnetically perturbed time-dependent density functional theory to magnetic circular dichroism. III. Temperature-dependent magnetic circular dichroism induced by spin-orbit coupling

“…[45][46][47] In most cases, the observed MCD of the X 3 M → A 3 ⌸ excitation has a derivative-shaped band shape with intensity that is strongly temperature-dependent indicating that the majority of the MCD intensity is due to C E terms. [45][46][47] In most cases, the observed MCD of the X 3 M → A 3 ⌸ excitation has a derivative-shaped band shape with intensity that is strongly temperature-dependent indicating that the majority of the MCD intensity is due to C E terms.…”