Showing papers by "Richard J. Saykally published in 1998"
TL;DR: The aΠu and bΠg States 2325 5.
Abstract: III. Formation of Carbon Clusters 2317 IV. Thermodynamic Properties 2319 V. C2 2319 A. Structure and Spectroscopy 2319 B. C2 2320 C. C2 2321 VI. C3 2321 A. Early Experimental Work 2321 B. Mid-IR and Far-IR Spectroscopy 2321 C. Electronic Spectroscopy 2323 1. The Σu + Ground State 2323 2. The AΠu State 2324 3. The Σu + State 2324 4. The aΠu and bΠg States 2325 5. Other Band Systems 2326 D. C3 in the Interstellar Medium 2326 E. C3 2326 F. C3 2327 VII. C4 2327 A. Theory 2327 B. Experiment 2328 1. The Rhombic Isomer 2328 2. The Linear Isomer 2328 C. Excited Electronic States 2330 D. C4 2331 E. C4 2332 VIII. C5 2332 A. Theory 2332 B. Experiment 2332 C. Excited Electronic States 2334 D. C5 2334 E. C5 2335 IX. C6 2335 A. Theory 2335 B. Experiment 2336 1. The Cyclic Isomer 2336 2. The Linear Isomer 2336 C. Excited Electronic States 2337 D. C6 2338 E. C6 2338 X. C7 2338 A. Theory 2338 B. Experiment 2338 C. Excited Electronic States 2340 D. C7 2340 E. C7 2340 XI. C8 2341 A. Theory 2341 B. Experiment 2342 1. The Cyclic Isomer 2342 2. The Linear Isomer 2342 C. Excited Electronic States 2342 D. C8 2342 E. C8 2342 XII. C9 2343 A. Theory 2343 B. Experiment 2343 C. Excited Electronic States 2345 D. C9 2345 E. C9 2345 XIII. C1
544 citations
TL;DR: In this paper, the authors performed a spectroscopic study of jet-cooled arginine using the novel technique of infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS).
Abstract: It is commonly thought that amino acids and peptides exist in a neutral configuration (protonated carboxylic acid and deprotonated amine) in the gas-phase1,2 because zwitterionic charge separation is unfavorable in the absence of solvation However, a recent report suggested that the most stable form of gaseous arginine is actually zwitterionic3 In this proposed configuration, the guanidine in the side chain serves as an intramolecular proton acceptor, whereas the carboxylic acid serves as the donor (cf Figure 1) We know of no previous direct experimental evidence that can support this intriguing claim and have accordingly performed a spectroscopic study of jet-cooled arginine using the novel technique of infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) Our results confirm that arginine indeed exists in the neutral configuration in a supersonic molecular beam The characterization of isolated gas-phase zwitterions is an important objective that has thus far proved elusive Detailed spectroscopic information would facilitate understanding of the structure and energetics of these systems, providing data that could be used to better parametrize biomolecular potential models4 Moreover, such studies constitute an essential starting point for investigating salient details of biomolecular solvation In infrared spectroscopy experiments, one could unambiguously identify the neutral form of arginine by the presence of carbonyl stretch bands at ca 1700 cm-1 and the zwitterion by carboxylate asymmetric and symmetric stretches at ca 1500-1600 cm-1 IR-CRLAS is a new ultrasensitive direct absorption technique that has recently been used to study a variety of molecular systems5-7 The method employs a set of highly reflective mirrors that form an optical cavity into which an absorbing sample can be placed The sample absorption is determined by monitoring the exponential intensity decay of laser radiation coupled into the cavity Resonant absorption will attenuate more light on each pass than does the passive cavity, leading to a faster decay of the light intensity By measuring the time constant of the exponential decay, one can directly extract the absolute absorbance of the sample Tuning the light over a given frequency range will thus produce an absorption spectrum Ultrahigh sensitivity results from the combination of a large path length and insensitivity to fluctuations in the total intensity Gas-phase arginine was produced using a heated, pulsed, 4-inch-slit molecular beam source, described previously8 The free base form of L-arginine (CAS 74-79-3) was obtained from Sigma No additional sample preparation was used Maintaining the source at a temperature ca 170 °C optimized the arginine signal After the experiment was run, a mass spectrum and FTIR spectrum (taken in a KBr pellet) of the sample remaining in the source as well as the residue collected on a microscope slide downstream of the source confirmed that the sample in the molecular beam did not undergo significant decomposition The IR-CRLAS spectrum of arginine in the 1550-1750 cm-1 region revealed two peaks near 1700 cm-1 (cf Figure 2; 1666 cm-1, 1693 cm-1), corresponding to a carbonyl stretch of a carboxylic acid and confirming that neutral arginine was present in our molecular beam The fact that several peaks were observed in this region can be explained by the presence of several nearly isoenergetic conformers Different structures led to distinct local environments and vibrational frequencies Similar patterns have been found in matrix isolation studies of other amino acids9 Scans near 1600 cm-1 showed no peaks Consequently, a significant population of zwitterions cannot be present in our molecular beam, assuming that the carboxylate mode intensity of the zwitterionic form of arginine is comparable to the carbonyl mode intensity of the neutral (1) Reva, I D; Plokhotnichenko, A M; Stepanian, S G; Ivanov, A Yu; Radchenko, E D; Sheina, G G; Blagoi, Y P Chem Phys Lett 1995, 232, 141-148 (2) Locke, M J; McIver, R T J Am Chem Soc 1983, 105, 4226-4232 (3) Price, W D; Jockusch, R A; Williams, E R J Am Chem Soc 1997, 119, 11988-11989 (4) Gregurick, S K; Fredj, E; Elber, R; Gerber, R B J Phys Chem B 1997, 101, 8595-8606 (5) Scherer, J J; Voelkel, D; Rakestraw, D J; Paul, J B; Collier, C P; Saykally, R J; O’Keefe, A Chem Phys Lett 1995, 245, 273-280 (6) Paul, J B; Collier, C P; Saykally, R J; Scherer, J J; O’Keefe, A J Phys Chem A 1997, 101, 5211-5214 (7) Paul, J B; Saykally, R J Anal Chem 1997, 69, A287-A292 (8) Liu, K; Fellers, R S; Viant, M R; McLaughlin, R P; Brown, M G; Saykally, R J ReV Sci Instrum 1997, 67, 410-416 (9) Reva, I D; Stepanian, S G; Plokhotnihenko, A M; Radchenko, E D; Sheina, G G; Blagoi, Yu P J Mol Struct 1994, 318, 1-13 Figure 1 Zwitterionic form of arginine Notice that this is not the standard zwitterion associated with biomolecules For this system, the guanidine in the side chain is the base, as opposed to the backbone amine of the amino acid
156 citations
TL;DR: A detailed description of the polycyclic aromatic hydrocarbon (PAH)/unidentified infrared band (UIR) mechanism is presented in which experimental spectral bandshape functions are used to simulate IR emission spectra for individual molecules.
Abstract: A detailed description of the polycyclic aromatic hydrocarbon (PAH)/unidentified infrared band (UIR) mechanism is presented in which experimental spectral bandshape functions are used to simulate IR emission spectra for individual molecules. These spectra are additively superimposed to produce a conglomerate spectrum representative of a family of PAH molecules. Ab initio vibrational frequencies and intensities for nine PAHs (neutral and cationic) as large as ovalene are used in conjunction with measured bandshape and temperature-dependent redshift data to simulate the UIR bands. The calculated spectra of cations provide a closer match to the UIRs than do those of the neutrals. However, the PAH cations used in the simulations fail to reproduce the details of the UIR emission spectra. The discrepancies are potentially alleviated if both larger PAHs and a greater number of PAHs were included in the simulation.
125 citations
TL;DR: In this article, it was shown that metal quantum dots can be treated as artificial atoms and crystallized into artificial solids that have electronic properties that can be tuned by controlling interpa...
Abstract: Recent work has shown that metal quantum dots can be treated as “artificial atoms” and crystallized into “artificial solids” that have electronic properties that can be tuned by controlling interpa...
97 citations
TL;DR: To obtain complete coverage of IR wavelengths relevant to the unidentified infrared bands (UIRs), UV laser-induced desorption was used to generate gas-phase highly excited PAHs and Lorentzian band shapes were convoluted with the monochromator-slit function in order to determine the widths of PAH emission bands under astrophysically relevant conditions.
Abstract: Single-photon infrared emission spectroscopy (SPIRES) has been used to measure emission spectra from polycyclic aromatic hydrocarbons (PAHs). A supersonic free-jet expansion has been used to provide emission spectra of rotationally cold and vibrationally excited naphthalene and benzene. Under these conditions, the observed width of the 3.3-micrometers (C-H stretch) band resembles the bandwidths observed in experiments in which emission is observed from naphthalene with higher rotational energy. To obtain complete coverage of IR wavelengths relevant to the unidentified infrared bands (UIRs), UV laser-induced desorption was used to generate gas-phase highly excited PAHs. Lorentzian band shapes were convoluted with the monochromator-slit function in order to determine the widths of PAH emission bands under astrophysically relevant conditions. Bandwidths were also extracted from bands consisting of multiple normal modes blended together. These parameters are grouped according to the functional groups mostly involved in the vibration, and mean bandwidths are obtained. These bandwidths are larger than the widths of the corresponding UIR bands. However, when the comparison is limited to the largest PAHs studied, the bandwidths are slightly smaller than the corresponding UIR bands. These parameters can be used to model emission spectra from PAH cations and cations of larger PAHs, which are better candidate carriers of the UIRs.
70 citations
TL;DR: In this article, the infrared O-D stretching spectrum of fully deuterated jet-cooled water clusters was measured using Raman-shifted pulsed dye laser spectroscopy.
Abstract: The infrared O–D stretching spectrum of fully deuterated jet-cooled water clusters is reported. Sequential red-shifts in the single donor O–D stretches, which characterize the cooperative effects in the hydrogen bond network, were accurately measured for clusters up to (D2O)8. Detailed comparisons with corresponding data obtained for (H2O)n clusters are presented. Additionally, rotational analyses of two D2O dimer bands are presented. These measurements were made possible by the advent of infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) using Raman-shifted pulsed dye lasers, which creates many new opportunities for gas phase IR spectroscopy.
69 citations
TL;DR: In this paper, the IR-CRLAS technique has been used to measure the mid-infrared O−D stretching spectrum of the fully deuterated gas-phase water dimer for the first time.
Abstract: The IR-CRLAS technique has been used to measure the mid-infrared O−D stretching spectrum of the fully deuterated gas-phase water dimer for the first time. The instrumentally limited resolution of 1...
60 citations
TL;DR: In this article, tunneling patterns observed in the vibration-rotation-tunnelling spectrum of (H2O)5 measured near 2.7 THz established the time scale for bifurcation rearrangements to be approximately 40 ns.
Abstract: Tunneling patterns observed in the vibration–rotation–tunnelling spectrum of (H2O)5 measured near 2.7 THz established the time scale for bifurcation rearrangements to be approximately 40 ns. This relatively local process is likely to be relevant in the dynamics of liquid water and ice.
48 citations
TL;DR: In this paper, the aΠu and bΠg States have been investigated in the presence of a Σu + ground state and a Πu+state state.
Abstract: III. Formation of Carbon Clusters 2317 IV. Thermodynamic Properties 2319 V. C2 2319 A. Structure and Spectroscopy 2319 B. C2 2320 C. C2 2321 VI. C3 2321 A. Early Experimental Work 2321 B. Mid-IR and Far-IR Spectroscopy 2321 C. Electronic Spectroscopy 2323 1. The Σu + Ground State 2323 2. The AΠu State 2324 3. The Σu + State 2324 4. The aΠu and bΠg States 2325 5. Other Band Systems 2326 D. C3 in the Interstellar Medium 2326 E. C3 2326 F. C3 2327 VII. C4 2327 A. Theory 2327 B. Experiment 2328 1. The Rhombic Isomer 2328 2. The Linear Isomer 2328 C. Excited Electronic States 2330 D. C4 2331 E. C4 2332 VIII. C5 2332 A. Theory 2332 B. Experiment 2332 C. Excited Electronic States 2334 D. C5 2334 E. C5 2335 IX. C6 2335 A. Theory 2335 B. Experiment 2336 1. The Cyclic Isomer 2336 2. The Linear Isomer 2336 C. Excited Electronic States 2337 D. C6 2338 E. C6 2338 X. C7 2338 A. Theory 2338 B. Experiment 2338 C. Excited Electronic States 2340 D. C7 2340 E. C7 2340 XI. C8 2341 A. Theory 2341 B. Experiment 2342 1. The Cyclic Isomer 2342 2. The Linear Isomer 2342 C. Excited Electronic States 2342 D. C8 2342 E. C8 2342 XII. C9 2343 A. Theory 2343 B. Experiment 2343 C. Excited Electronic States 2345 D. C9 2345 E. C9 2345 XIII. C1
20 citations
TL;DR: In this paper, the tungsten isotopic structure in the W 16 O F −X 0-0 transition at 23405 cm−1 is clearly resolved, and its analysis reveals that the strong interstate interactions previously reported in the matrix are also present in the free molecule in the gas phase.
19 citations
TL;DR: In this paper, the ground-state C-rotational constant is estimated to be 975±60 MHz, consistent with ab initio structural predictions, and the precisely determined B -rotational constants (B =1750.96±0.20 MHz) agree well with previous results.
TL;DR: In this paper, the low-lying electronic states of SiCu, SiCu+ and SiCu− have been studied using a variety of high-level ab initio techniques.
Abstract: The low-lying electronic states of SiCu, SiCu^+, and SiCu^− have been studied using a variety of high-level ab initio techniques. As expected on the basis of simple orbital occupancy and bond forming for Si(s^2p^2)+Cu(s^1) species, ^2Π_r, ^1Σ^+, and ^3Σ^− states were found to be the ground electronic states for SiCu, SiCu^+, and SiCu^−, respectively; the ^2Π_r state is not that suggested in most recent experimental studies. All of these molecules were found to be quite strongly bound although the bond lengths, bond energies, and harmonic frequencies vary slightly among them, as a result of the nonbonding character of the 2π-MO (molecular orbital) [composed almost entirely of the Si 3p-AO (atomic orbital)], the occupation of which varies from 0 to 2 within the ^1Σ^+, ^2Π_r, and ^3Σ^− series. The neutral SiCu is found to have bound excited electronic states of ^4Σ^−, ^2Δ, ^2Σ^+, and ^2Π_i symmetry lying 0.5, 1.2, 1.8, and 3.2 eV above the ^2Π_r ground state. It is possible but not yet certain that the ^2Π_i state is, in fact, the “B state” observed in the recent experimental studies by Scherer, Paul, Collier, and Saykally.
01 Jan 1998
TL;DR: Paul, R.B. Provencal, and R.J. Saykally as mentioned in this paper, Anal. Chem. Phys. 69, 287A (1997), published in 1997.
Abstract: $^{a}$J.B. Paul, and R.J. Saykally, Anal. Chem. 69, 287A (1997). $^{b}$J.B. Paul, R.A. Provencal, and R.J. Saykally. J. Phys. Chem. in press.
Journal Article•
TL;DR: The technique is used to study general trace analysis, free radicals in flames and chemical reactors, molecular ions in electrical discharges, biological molecules and water clusters in supersonic jets, and vibrational overtones of stable molecules.
Abstract: NASA: Technology associated with cavity ringdown laser absorption spectroscopy is reviewed. The technique is used to study general trace analysis, free radicals in flames and chemical reactors, molecular ions in electrical discharges, biological molecules and water clusters in supersonic jets, and vibrational overtones of stable molecules. Its specific enough to detect about 1-ppm fractional absorption by a gaseous sample in about 10 microseconds. The use of mirrors in ringdown sepctroscopy is explained. Other topics include the generation of pulsed infrared rays and the adaptation of ringdown spectroscopy for use with narrow-bandwidth continuous-wave lasers.
01 Jan 1998
TL;DR: In this article, the ground-state VRT spectrum of a low-frequency intermolecular vibration of D O was recorded and the relative intensities in the compact Q-branch region were analyzed.
Abstract: The vibration–rotation–tunneling VRT spectrum of a low-frequency intermolecular vibration of D O was recorded. . 25 near 0.9 THz 30.2 cm . From an analysis of the relative intensities in the compact Q-branch region, the ground-state y1 .C-rotational constant is estimated to be 975"60 MHz, consistent with ab initio structural predictions. The preciselydetermined B-rotational constant.Bs1750.96"0.20 MHz agrees well with previous results. Efforts to resolve possiblebifurcation tunneling fine structure, such as that observed in VRT spectra of D O , revealed no such effects. This. 23 constrains the splittings to be less than 450 kHz, or roughly 3 times smaller than required by previous results. q1998Published by Elsevier Science B.V. All rights reserved. 1. IntroductionPentagonal rings of water molecules appear to beubiquitous in nature. Clathrate hydrates and solvationof hydrophobic groups in proteins and DNA are two ) Corresponding author. E-mail: saykally@cchem.berkeley.edu