MIT Reports to the President 1999–2000
The George Russell Harrison Spectroscopy Laboratory is engaged in research in the field of modern optics and spectroscopy for the purpose of furthering fundamental knowledge of atoms and molecules and pursuing advanced engineering and biomedical applications. Professor Michael S. Feld is Director; Professor Jeffrey I. Steinfeld and Dr. Ramachandra R. Dasari are Associate Directors. An Interdepartmental Laboratory, the Spectroscopy Laboratory encourages participation and collaboration among researchers in various disciplines of science and engineering. Professors Moungi G. Bawendi, Feld, Robert W. Field, Daniel Kleppner, Stephen J. Lippard, Keith A. Nelson, Steinfeld, Toyoichi Tanaka, Steven R. Tannenbaum and Dr. Dasari are core investigators.
The Laboratory operates two laser resource facilities. The MIT Laser Biomedical Research Center (LBRC), a Biotechnology Resource Center of the National Institutes of Health, develops basic scientific understanding, new techniques and technology for advanced biomedical applications of lasers; core, collaborative and outside research are conducted. The National Science Foundation-supported MIT Laser Research Facility (LRF) provides resources for core research programs in the physical sciences for 13 MIT Chemistry and Physics faculty. Information about the equipment and facilities of the LRF and the LBRC can be found in the Spectroscopy Laboratory Researcher’s Guide.
Professor Field and his associates have predicted and observed the spectroscopic signature of "local-bender" states in the first singlet electronic excited state of C2H2. These studies will permit direct sampling of the region of the isomerization barrier between acetylene and vinylidene, thus promote systematic characterization of the lowest vibrational "levels" (10^-12 second lifetime) of vinylidene. They were also able to disentangle overlapping spectral patterns in the Dispersed Florescence Spectrum of 13C2H2, from which they could construct a complete description of the intramolecular vibrational redistribution processes. Using a hybrid robust estimator/least squares baseline removal routine devised by Dr. Matthew Jacobson, the Dispersed Florescence spectrum may be recovered, free of corruption by the underlying collisionally-generated baseline. Another ongoing project, a collaboration with Dr. Stephen Coy, involves kinetic modelling of K-changing collisional processes in the acetylene S_1 state. Another major project, conducted by Dr. Manjula Canagaratna and others, is to characterize the structure and nonradiative dynamics of the triplet electronic states in acetylene and to gain insight into radiationless relaxation mechanisms in small polyatomic molecules. Surface-electron-ejection-by-laser-excited-metastables (SEELEM) and laser-induced fluorescence (LIF) are the detection techniques used in this project. A second-generation experimental apparatus, which consists of a doubly-differentially pumped molecular beam machine, has recently been put into operation.
Professors Field and Steinfeld, in collaboration with Drs. Shengfu Yang, Manjula Canagaratna, and Alexander Kachanov, have used IntraCavity Laser Absorption Spectroscopy (ICLAS) and made careful measurement of line intensities and self-broadening coefficients in the oxygen A-band, showing that ICLAS can be a reliable method for obtaining these parameters for weakly absorbing transitions. Measurements have also been carried out on the 3n 1 overtone band of HONO, an important atmospheric trace species. Using a double-time-correlated ICLAS technique, we have succeeded in detecting photolysis products resulting from the flash-decomposition of acrylonitrile.
Professor Bawendi and Drs. Robert Neuhauser and Hans-Jurgen Eisler have designed and developed an apparatus for the highly parallel study of the spectroscopy of individual quantum dots. This allows hundreds of dots to be observed simultaneously in both image and spectral mode. A correlation between fluorescence intermittency and spectral diffusion was observed. Fluorescence polarization studies showed that far-field polarization microscopy can determine the 3 dimensional orientation of individual quantum dots.
Professor Mildred Dresselhaus and Drs. Gene Dresselhaus, Katrin Kneipp, Paola Corio, Alessandra Marucci, and Ado Jorio Vasconcelos have used resonance Raman spectroscopy to study the different characteristic Raman lineshapes associated with metallic or semiconducting carbon nanotubes. The use of surface enhanced Raman spectroscopy techniques was shown to increase the Raman signal by many orders of magnitude. Polarization studies allowed the assignment of the Raman mode symmetries. Further experiments are now in progress to characterize the depolarization effect in metallic carbon nanotubes.
Professor Feld and Drs. Dasari and Chung-Chieh Yu have investigated the effect of having more than one atom at a time present in the cavity on cavity-QED laser by using quantum trajectory simulations. They also have developed a novel apparatus for measuring the degree of second-order coherence g2(t) of the microlaser output. Data for the correlation time is compared with theoretical predictions.
Professors Tanaka and Feld have demonstrated that frustrations of interactions within collapsed polymer gel structures were shown to have been successfully diminished through a synthesis method we call imprinting. UV and fluorescence spectroscopy showed the polymers created in this way were indeed memorizing an aspect of their conformation. This constitutes an important step in the creation of artificial proteins.
Professor Stephen J. Lippard and Dr. Yuji Mikata have developed an efficient method for photocross-linking between cisplatin-modified DNA and damage-recognition proteins using the laser as an irradiation source. There was non DNA-DAN interstrand cross-linking, which had been found upon irradiation with a transilluminator at 302 nm. In another project, Professor Lippard and his associates have used resonance Raman spectroscopy to characterize the interaction of dioxygen and hydrogen peroxide with diiron(II) complexes. The diiron(II) compounds have been synthesized as models for the active sites of dioygen-activating metalloenzymes including hemerythrin, methane monooxygenase, alkane desaturases and ribonucleotide reductase.
Drs. Jayanti Pande and Eugene Hanlon are investigating the role of individual cysteine residues of the eye lens protein g B crystallin, on the oxidation, aggregation and phase separation properties of the protein. Raman spectra of several recombinant g Bcrystallin mutants, each with a single point mutation of Cys to Ser suggest that the wild type and mutant proteins are closely similar in their secondary structure and in the environment of thiol groups.
Professor Tannenbaum and Drs. Paul Skipper, Can Özbal and Dasari have further developed a method using ultrasensitive HPLC with laser-induced fluorescence detection. Preliminary epidemiological experiments quantifying benzo[a]pyrene adducts in human plasma have shown that the consumption of meat products may be a possible source of exposure to this carcinogen.
Professor Jonathan King and Drs. Stephen Raso and Hanlon are using Raman spectroscopy to monitor conformational changes in the protein granulocyte-colony stimulating factor (G-CSF) by monitoring changes in the SH stretch and amides I and III. G-CSF is an important therapeutic agent, but drug delivery is hampered by the protein’s propensity to precipitate under physiological conditions.
Professor Alexander Rich and Drs. Bernard Brown and Hanlon have used solution-state Raman spectroscopy to observe the left-handed Z conformation of RNAs complexed with the Za domain of the human RNA editing enzyme ADAR1. These experiments have conclusively demonstrated that the Za peptide binds RNA molecules in a Z-conformation-dependent manner.
The Tokmakoff group has designed and built a cavity-dumped Ti:sapphire laser capable of producing light pulses as short as 15 femtoseconds. The laser has been used to observe the short time dynamics of liquids such as carbon disulfide, acetonitrile, and water through time-resolved coherent Raman spectroscopy. Work has begun to fabricate a multipass amplifier and OPA capable of generating femtosecond mid-IR pulses, which will be used to investigate vibrational dynamics of liquids and proteins in solution.
Professor Feld and Drs. Dasari, Georgakoudi, Gurjar, Hanlon, Itzkan, Perelman, and Wax are pursuing basic and applied applications of lasers and spectroscopy in biology and medicine. Fluorescence, reflectance, near-IR Raman, and light scattering spectroscopy and low coherence interferometry are being used for histological and biochemical analysis of tissues and diagnosis of disease. Clinical studies are being conducted with researchers from the Cleveland Clinic Foundation, Brigham and Women’s Hospital, Metrowest Hospital, Beth Israel Hospital and New England Medical Center. Recent developments include: new technique for extracting undistorted tissue fluorescence using combination of fluorescence and reflectance; development of light scattering spectroscopy-based functional imaging system to detect the precancerous changes in epithelial tissues; development of phase dispersion microscopy and tomography which are based on two-wavelength low coherence interferometric measurements; and fluorescence spectroscopy of brain tissue to identify Alzheimer’s disease. The experimental and theoretical work of this program is advancing new laser diagnostic technologies in the field of medicine.
More information about the laboratory can be found on the World Wide Web at http://web.mit.edu/spectroscopy/.
Michael S. Feld
MIT Reports to the President 1999–2000