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Infrared data in the nu(CO) region (1800-2150 cm(-1), in acetonitrile at 298 K) are reported for the ground (nu(gs)) and polypyridyl-based, metal-to-ligand charge-transfer (MLCT) excited (nu(es)) states of cis-[Os(pp)2(CO)(L)](n)(+) (pp = 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy); L = PPh3, CH(3)CN, pyridine, Cl, or H) and fac-[Re(pp)(CO)3(4-Etpy)](+) (pp = phen, bpy, 4,4'-(CH3)2bpy, 4,4'-(CH3O)2bpy, or 4,4'-(CO2Et)2bpy; 4-Etpy = 4-ethylpyridine). Systematic variations in nu(gs), nu(es), and Delta(nu) (Delta(nu) = nu(es) - nu(gs)) are observed with the excited-to-ground-state energy gap (E(0)) derived by a Franck-Condon analysis of emission spectra. These variations can be explained qualitatively by invoking a series of electronic interactions. Variations in dpi(M)-pi(CO) back-bonding are important in the ground state. In the excited state, the important interactions are (1) loss of back-bonding and sigma(M-CO) bond polarization, (2) pi(pp*-)-pi(CO) mixing, which provides the orbital basis for mixing pi(CO)- and pi(4,4'-X(2)bpy)-based MLCT excited states, and (3) dpi(M)-pi(pp) mixing, which provides the orbital basis for mixing pipi- and pi(4,4'-X(2)bpy*-)-based MLCT states. The results of density functional theory (DFT) calculations on the ground and excited states of fac-[Re(I)(bpy)(CO)3(4-Etpy)](+) provide assignments for the nu(CO) modes in the MLCT excited state. They also support the importance of pi(4,4'-X2bpy*-)-pi(CO) mixing, provide an explanation for the relative intensities of the A'(2) and A' ' excited-state bands, and provide an explanation for the large excited-to-ground-state nu(CO) shift for the A'(2) mode and its relative insensitivity to variations in X.

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Resonance Raman spectra of the single-copper blue proteins azurin (from the bacteria Pseudomonas putida, Pseudomonas aeruginosa, Iwasaki sp., Bortadella pertussis, Bortadella bronchiseptica, and Alcaligenes faecalis), plastocyanin (from French bean and spinach), and stellacyanin (from the Japanese and Chinese lacquer trees Rhus vernicifera) and the multicopper oxidases lacease (from the fungus Polyporus versicolor and the Japanese and Chinese lacquer trees), ascorbate oxidase (from zucchini squash), and ceruloplasmin (from human blood serum) are reported. Cryoresonance Raman observations (10-77 K) are reported for selected azurins, stellacyanin, the plastocyanins, and the laceases. Isotope studies employing 63Cu/65Cu and H/D substitution are reported for selected azurins and stellacyanin, allowing identification of modes having significant

Characteristic patterns of infrared bands in the ν(CO) region have been observed in the time-resolved infrared (TRIR) spectra of fac-rhenium tricarbonyl complexes that allow for identification of transient states that result following laser flash excitation. These patterns can be interpreted by combining experimental TRIR data with density functional theory (DFT) calculations. The DFT calculations are particularly valuable as they provide vibrational energy shifts between the ground and excited states and an analysis of the electronic interactions in terms of the orbitals involved in the excitation. TRIR and DFT results for four different transient excited states, intraligand π f π*, metal-to-ligand charge transfer (MLCT), intramolecular (dπ-Οπ) f π* excited states, and a redox-separated (RS state), are presented here. A unique example of competing excited states studied by TRIR is also presented. The complexes studied include fac-[Re I (CO) 3 (Me 2 dppz)(4-Etpy)] + , fac-[Re I (CO) 3 (bpy)(4-Etpy)] + , fac-[Re I (CO) 3 (4,4′-(CH 3 ) 2 bpy)(OQD)] , fac-[Re I (CO) 3 (Me 2 dppz)(py-PTZ)] + , and fac-[Re I (CO) 3 (dppz)(py-PTZ)] + (Me 2 dppz is dimethyl dipyrido[3,2-a:2′,3′-c]phenazine; dppz is dipyrido-[3,2-a:2′,3′-c]phenazine; 4Etpy is 4-ethylpyridine; bpy is 2,2′-bipyridine; 4,4′-(CH 3 ) 2 bpy is 4,4′-(CH 3 )-2,2′bipyridine; OQD is 1-methyl-6-oxyquinone; py-PTZ is 10-(4-picolyl)phenothiazine). In addition to the DFT studies on the lowest triplet states probed by TRIR spectroscopy, time-dependent DFT (TD-DFT) calculations were also performed to analyze several of the lowest singlet and triplet excited states for each of the complexes.

as a technical staff member in 1993. He is currently part of the Chemical Science and Technology Division at Los Alamos. His research has focused on the development and application of vibrational spectroscopy with the goal of understanding complex chemical problems. This includes studies involving time-resolved vibrational spectroscopy and, more recently, vibrational microspectroscopy and imaging.

The first time-resolved infrared difference spectra for metal-to-ligand charge transfer (MLCT) excited states in the fingerprint region from 1400 to 1625 cm-1 are reported for [Ru(bpy)3]2+* and [Re(bpy)(CO)3(4-Etpy)]+* in CD3CN at 298 K (bpy is 2,2‘-bipyridine; 4-Etpy is 4-ethylpyridine). The spectra are assigned by comparison to ground-state spectra and electrochemically generated [RuIII(bpy)3]3+ and [RuII(bpy•-)(bpy)2]+. The data provide clear evidence for the localized description [RuIII(bpy•-)(bpy)2]2+* on the ∼100 ns time scale. They also give insight into electronic distribution in the excited state based on the magnitudes and directions of the infrared shifts.