Spectroscopy of free radicals and radical containing entrance-channel complexes in superfluid helium nano-droplets

The spectroscopy of free radicals and radical containing entrance-channel complexes embedded in superfluid helium nano-droplets is reviewed. The collection of dopants inside individual droplets in the beam represents a micro-canonical ensemble, and as such each droplet may be considered an isolated cryo-reactor. The unique properties of the droplets, namely their low temperature (0.4 K) and fast cooling rates ($\sim10^{16}$ K s$^{-1}$) provides novel opportunities for the formation and high-resolution studies of molecular complexes containing one or more free radicals. The production methods of radicals are discussed in light of their applicability for embedding the radicals in helium droplets. The spectroscopic studies performed to date on molecular radicals and on entrance / exit-channel complexes of radicals with stable molecules are detailed. The observed complexes provide new information on the potential energy surfaces of several fundamental chemical reactions and on the intermolecular interactions present in open-shell systems. Prospects of further experiments of radicals embedded in helium droplets are discussed, especially the possibilities to prepare and study high-energy structures and their controlled manipulation, as well as the possibility of fundamental physics experiments.Comment: 25 pages, 12 figures, 4 tables (RevTeX

A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets

Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\Sigma_{1/2}$ and $^{2}\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, motivated by preliminary spectroscopic evidence for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular halogen HCN-X$_{2}$ complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe

Entrance Channel X-HF (X=Cl, Br, and I) Complexes studied by High-Resolution Infrared Laser Spectroscopy in Helium Nanodroplets

Rotationally resolved infrared spectra are reported for halogen atom - HF free radical complexes formed in helium nanodroplets. An effusive pyrolysis source is used to dope helium droplets with Cl, Br and I atoms, formed by thermal dissociation of Cl$_2$, Br$_2$ and I$_2$. A single hydrogen fluoride molecule is then added to the droplets, resulting in the formation of the X-HF complexes of interest. Analysis of the resulting spectra confirms that the observed species have $^2\Pi_{3/2}$ ground electronic states, consistent with the linear hydrogen bound structures predicted from theory. Stark spectra are also reported for these species, from which the permanent electric dipole moments are determined.Comment: 41 pages, 16 figures, 5 table

Steroid Non-Responsive Optic Neuropathy (Presentation Video)

Loss of vision OUA 75-year old with painless, progressive loss of vision. Previous history significant for BPH and excised skin malignant melanoma.VA: Initial - 20/50 OD, 20/25 OS; Color plates: 6/12 OD, 12/12 OS; Follow-up - 20/70 OD, 20/120 OS; Color plates: 1/12 OD, 0/12 OS; RAPD OSMRIGlomeruloid vascular proliferation; Cells positive for glial fibrillary astrocytic protein consistent with glioblastoma multiforme.Corticosteroids; Surgery; XRT1. Millar WS, Tartaglino LM, Sergott RC, Freidman DP and Flanders AE: MR of Malignant Optic Glioma of Adulthood. AJNR 16:1673-1676, 1995. 2. Freidman DP and Hollander MD: Neuroradiology Case of the Day. RadioGraphics 18: 1046-1048, 1998. 3. Wabbels B, Demmler A, Seitz J et al: Unilateral adult malignant optic nerve glioma. Graefe's Arch Clin Exp Ophthalmol 242:741-748, 2004. 4. Hoyt WF, Meshel LG, Lessell S and al:Malignant Optic Glioma of Adulthood. Brain 96: 121-132, 1973

Steroid Non-Responsive Optic Neuropathy (PowerPoint)

Loss of vision OUA 75-year old male with painless, progressive loss of vision. Previous history significant for BPH and excised skin malignant melanoma.VA: Initial - 20/50 OD, 20/25 OS; color plates: 6/12 OD, 12/12 OS; Follow-up - 20/70 OD, 20/120 OS; Color plates: 1/12 OD, 0/12 OS; RAPD OSMRIGlomeruloid vascular proliferation; Cells positive for glial fibrillary astrocytic protein consistent with glioblastoma multiforme.Corticosteroids; Surgery XRT1. Millar WS, Tartaglino LM, Sergott RC, Freidman DP and Flanders AE: MR of Malignant Optic Glioma of Adulthood. AJNR 16:1673-1676, 1995. 2. Freidman DP and Hollander MD: Neuroradiology Case of the Day. RadioGraphics 18: 1046-1048, 1998. 3. Wabbels B, Demmler A, Seitz J et al: Unilateral adult malignant optic nerve glioma. Graefe's Arch Clin Exp Ophthalmol 242:741-748, 2004. 4. Hoyt WF, Meshel LG, Lessell S and al:Malignant Optic Glioma of Adulthood. Brain 96: 121-132, 1973

Diagnosis of Inclusion (PowerPoint)

Headache; Fever; LethargyA 50-year old female with a 2-day history of headache and fever found unresponsive at home.VA: 20/50 OU; RAPD OSMRINecrotic brain parenchyma with focal hemorrhages; Scattered neutrophils; Perivascular lymphocytesAntiviral agents1. Whitley et al JAMA 1982 247:317-20. Utley et al Neuropsychiatry Neuropsychol Behav Neurol 1997;10:180-189. 2. Morris et al Br J Clin Psychol 1995 34:571-6. Love S, Wiley CA. Viral Diseases. In: Graham DI, Lantos PL, eds. Greenfield's Neuropathology, Vol. II London: Arnold, 2002; 18-23. 3. Tien et al AJR 1993 161:167. Soo et al Am J Roentgenol 1993 160:1089-93