Flow-Tube Investigations of Hypergolic Reactions of a Dicyanamide Ionic Liquid Via Tunable Vacuum Ultraviolet Aerosol Mass Spectrometry.

The unusually high heats of vaporization of room-temperature ionic liquids (RTILs) complicate the utilization of thermal evaporation to study ionic liquid reactivity. Although effusion of RTILs into a reaction flow-tube or mass spectrometer is possible, competition between vaporization and thermal decomposition of the RTIL can greatly increase the complexity of the observed reaction products. In order to investigate the reaction kinetics of a hypergolic RTIL, 1-butyl-3-methylimidazolium dicyanamide (BMIM+DCA-) was aerosolized and reacted with gaseous nitric acid, and the products were monitored via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry at the Chemical Dynamics Beamline 9.0.2 at the Advanced Light Source. Reaction product formation at m/z 42, 43, 44, 67, 85, 126, and higher masses was observed as a function of HNO3 exposure. The identities of the product species were assigned to the masses on the basis of their ionization energies. The observed exposure profile of the m/z 67 signal suggests that the excess gaseous HNO3 initiates rapid reactions near the surface of the RTIL aerosol. Nonreactive molecular dynamics simulations support this observation, suggesting that diffusion within the particle may be a limiting step. The mechanism is consistent with previous reports that nitric acid forms protonated dicyanamide species in the first step of the reaction.

Stable and high-power few cycle supercontinuum for 2D ultrabroadband electronic spectroscopy.

Broadband supercontinuum (SC) pulses in the few cycle regime are a promising source for spectroscopic and imaging applications. However, SC sources are plagued by poor stability, greatly limiting their utility in phase-resolved nonlinear experiments such as 2D photon echo spectroscopy (2D PES). Here, we generated SC by two-stage filamentation in argon and air starting from 100 fs input pulses, which are sufficiently high-power and stable to record time-resolved 2D PE spectra in a single laser shot. We obtain a total power of 400 µJ/pulse in the visible spectral range of 500-850 nm and, after compression, yield pulses with duration of 6 fs according to transient-grating frequency-resolved optical gating (TG-FROG) measurements. We demonstrate the method on the laser dye, Cresyl Violet, and observe coherent oscillations indicative of nuclear wavepacket dynamics.

Thermal decomposition mechanisms of alkylimidazolium ionic liquids with cyano-functionalized anions.

Because of the unusually high heats of vaporization of room-temperature ionic liquids (RTILs), volatilization of RTILs through thermal decomposition and vaporization of the decomposition products can be significant. Upon heating of cyano-functionalized anionic RTILs in vacuum, their gaseous products were detected experimentally via tunable vacuum ultraviolet photoionization mass spectrometry performed at the Chemical Dynamics Beamline 9.0.2 at the Advanced Light Source. Experimental evidence for di- and trialkylimidazolium cations and cyano-functionalized anionic RTILs confirms thermal decomposition occurs primarily through two pathways: deprotonation of the cation by the anion and dealkylation of the imidazolium cation by the anion. Secondary reactions include possible cyclization of the cation and C2 substitution on the imidazolium, and their proposed reaction mechanisms are introduced here. Additional evidence supporting these mechanisms was obtained using thermal gravimetric analysis-mass spectrometry, gas chromatography-mass spectrometry, and temperature-jump infrared spectroscopy. In order to predict the overall thermal stability in these ionic liquids, the ability to accurately calculate both the basicity of the anions and their nucleophilicity in the ionic liquid is critical. Both gas phase and condensed phase (generic ionic liquid (GIL) model) density functional theory calculations support the decomposition mechanisms, and the GIL model could provide a highly accurate means to determine thermal stabilities for ionic liquids in general.

Thermal decomposition mechanism of 1-ethyl-3-methylimidazolium bromide ionic liquid.

In order to better understand the volatilization process for ionic liquids, the vapor evolved from heating the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIM(+)Br(-)) was analyzed via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and thermogravimetric analysis mass spectrometry (TGA-MS). For this ionic liquid, the experimental results indicate that vaporization takes place via the evolution of alkyl bromides and alkylimidazoles, presumably through alkyl abstraction via an S(N)2 type mechanism, and that vaporization of intact ion pairs or the formation of carbenes is negligible. Activation enthalpies for the formation of the methyl and ethyl bromides were evaluated experimentally, ΔH(‡)(CH(3)Br) = 116.1 ± 6.6 kJ/mol and ΔH(‡)(CH(3)CH(2)Br) = 122.9 ± 7.2 kJ/mol, and the results are found to be in agreement with calculated values for the S(N)2 reactions. Comparisons of product photoionization efficiency (PIE) curves with literature data are in good agreement, and ab initio thermodynamics calculations are presented as further evidence for the proposed thermal decomposition mechanism. Estimates for the enthalpy of vaporization of EMIM(+)Br(-) and, by comparison, 1-butyl-3-methylimidazolium bromide (BMIM(+)Br(-)) from molecular dynamics calculations and their gas phase enthalpies of formation obtained by G4 calculations yield estimates for the ionic liquids' enthalpies of formation in the liquid phase: ΔH(vap)(298 K) (EMIM(+)Br(-)) = 168 ± 20 kJ/mol, ΔH(f, gas)(298 K) (EMIM(+)Br(-)) = 38.4 ± 10 kJ/mol, ΔH(f, liq)(298 K) (EMIM(+)Br(-)) = -130 ± 22 kJ/mol, ΔH(f, gas)(298 K) (BMIM(+)Br(-)) = -5.6 ± 10 kJ/mol, and ΔH(f, liq)(298 K) (BMIM(+)Br(-)) = -180 ± 20 kJ/mol.

Ultrafast decay of superexcited c 4Σu- nlσg v=0,1 states of O2 probed with femtosecond photoelectron spectroscopy.

Neutral superexcited states in molecular oxygen converging to the O(2)(+) c (4)Σ(u)(-) ion state are excited and probed with femtosecond time-resolved photoelectron spectroscopy to investigate predissociation and autoionization relaxation channels as the superexcited states decay. The c (4)Σ(u)(-) 4sσ(g) v=0, c (4)Σ(u)(-) 4sσ(g) v=1, and c (4)Σ(u)(-) 3dσ(g) v=1 superexcited states are prepared with pulsed high-harmonic radiation centered at 23.10 eV. A time-delayed 805 nm laser pulse is used to probe the excited molecular states and neutral atomic fragments by ionization; the ejected photoelectrons from these states are spectrally resolved with a velocity map imaging spectrometer. Three excited neutral O* atom products are identified in the photoelectron spectrum as 4d(1) (3)D(J)°, 4p(1) (5)P(J)° and 3d(1) (3)D(J)° fragments. Additionally, several features in the photoelectron spectrum are assigned to photoionization of the transiently populated superexcited states. Using principles of the ion core dissociation model, the atomic fragments measured are correlated with the molecular superexcited states from which they originate. The 4d(1) (3)D(J)° fragment is observed to be formed on a timescale of 65 ± 5 fs and is likely a photoproduct of the 4sσ(g) v = 1 state. The 4p(1) (5)P(J)° fragment is formed on a timescale of 427 ± 75 fs and correlated with the neutral predissociation of the 4sσ(g) v = 0 state. The timescales represent the sum of predissociation and autoionization decay rates for the respective superexcited state. The production of the 3d(1) (3)D(J)° fragment is not unambiguously resolved in time due to an overlapping decay of a v = 1 superexcited state photoelectron signal. The observed 65 fs timescale is in good agreement with previous experiments and theory on the predissociation lifetimes of the v = 1 ion state, suggesting that predissociation may dominate the decay dynamics from the v = 1 superexcited states. An unidentified molecular state is inferred by the detection of a long-lived depletion signal (reduction in autoionization) associated with the B (2)Σ(g)(-) ion state that persists up to time delays of 105 ps.

Soft ionization of thermally evaporated hypergolic ionic liquid aerosols.

Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim(+)][Tf(2)N(-)]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim(+)][Dca(-)]), are generated by vaporizing ionic liquid submicrometer aerosol particles for the first time; the vaporized species are investigated by dissociative ionization with tunable vacuum ultraviolet (VUV) light, exhibiting clear intact cations, Emim(+) and Bmim(+), presumably originating from intact ion pairs. Mass spectra of ion pair vapor from an effusive source of the hypergolic ionic liquid show substantial reactive decomposition due to the internal energy of the molecules emanating from the source. Photoionization efficiency curves in the near threshold ionization region of isolated ion pairs of [Emim(+)][Tf(2)N(-)] ionic liquid vapor are compared for an aerosol source and an effusive source, revealing changes in the appearance energy due to the amount of internal energy in the ion pairs. The aerosol source has a shift to higher threshold energy (∼0.3 eV), attributed to reduced internal energy of the isolated ion pairs. The method of ionic liquid submicrometer aerosol particle vaporization, for reactive ionic liquids such as hypergolic species, is a convenient, thermally "cooler" source of isolated intact ion pairs in the gas phase compared to effusive sources.

Tunable wavelength soft photoionization of ionic liquid vapors.

Combined data of photoelectron spectra and photoionization efficiency curves in the near threshold ionization region of isolated ion pairs from [emim][Tf(2)N], [emim][Pf(2)N], and [dmpim][Tf(2)N] ionic liquid vapors reveal small shifts in the ionization energies of ion-pair systems due to cation and anion substitutions. Shifts toward higher binding energy following anion substitution are attributed to increased electronegativity of the anion itself, whereas shifts toward lower binding energies following cation substitution are attributed to an increase in the cation-anion distance that causes a lower Coulombic binding potential. The predominant ionization mechanism in the near threshold photon energy region is identified as dissociative ionization, involving the dissociation of the ion pair and the production of intact cations as the positively charged products.

Heteroleptic nickel(ii)-diNHC complexes and an unusual 'reverse' carbene-transfer reaction to silver(i).

A series of rare [NiX2(MeCCprop)] complexes bearing the cis-chelating benzimidazole-derived dicarbene ligand MeCCprop and varying anionic coligands (2, X = N3; 3, X = NCS; 4, X = I; 5, X = O2CCF3) have been prepared and coligand dependent structural and spectroscopic features have been evaluated. This study also revealed an unusual 'reverse' carbene transfer reaction from nickel to silver giving the disilver species [Ag2X2(µ-κ2-MeCCprop)] (6, X = OAc; 7, X = O2CCF3). A preliminary catalytic study of two representative NiII diNHC complexes in the aqueous and phosphine-free Suzuki-Miyaura coupling reaction of aryl halides is reported as well. These reactions provide good yields of coupling products, but do not require inert conditions.

Age-related impairments in the revision of syntactic misanalyses: effects of prosody.

Two experiments examined whether young and older adults differ in comprehending sentences that contain temporary syntactic closure ambiguities. Experiment 1 examined age-related differences using the Auditory Moving Window (AMW) task, in which sentences were presented in a segment-by-segment self-paced fashion. Experiment 2 examined age-related differences using a sentence recall task, in which sentences were presented in their entirety. Sentences were constructed to have cooperating prosody (i.e., where prosody is consistent with the syntactic boundaries), baseline prosody (i.e., where prosody is ambiguous in the syntactically ambiguous region), and conflicting prosody (i.e., where cross-splicing relocates the prosodic phrase break at a misleading point in syntactic structure). The results showed that both young and older adults make comparable use of prosodic information to interpret temporary syntactic ambiguities, although younger adults may make use of this information more quickly than older adults. In addition, older adults appeared to be less able than young adults to revise initial syntactic misinterpretations caused by conflicting prosodic information. These results are interpreted with respect to age-related impairments in the allocation of working memory resources and inefficient inhibitory function during spoken language processing.

Neurophysiology and neuroanatomy of pitch perception: auditory cortex.

We present original results and review literature from the past fifty years that address the role of primate auditory cortex in the following perceptual capacities: (1) the ability to perceive small differences between the pitches of two successive tones; (2) the ability to perceive the sign (i.e., direction) of the pitch difference [higher (+) vs. lower (-)]; and (3) the ability to abstract pitch constancy across changes in stimulus acoustics. Cortical mechanisms mediating pitch perception are discussed with respect to (1) gross and microanatomical distribution; and (2) candidate neural coding schemes. Observations by us and others suggest that (1) frequency-selective neurons in primary auditory cortex (A1) and surrounding fields play a critical role in fine-grained pitch discrimination at the perceptual level; (2) cortical mechanisms that detect pitch differences are neuroanatomically dissociable from those mediating pitch direction discrimination; (3) cortical mechanisms mediating perception of the "missing fundamental frequency (F0)" are neuroanatomically dissociable from those mediating pitch perception when F0 is present; (4) frequency-selective neurons in both right and left A1 contribute to pitch change detection and pitch direction discrimination; (5) frequency-selective neurons in right A1 are necessary for normal pitch direction discrimination; (6) simple codes for pitch that are based on single- and multiunit firing rates of frequency-selective neurons face both a "hyperacuity problem" and a "pitch constancy problem"-that is, frequency discrimination thresholds for pitch change direction and pitch direction discrimination are much smaller than neural tuning curves predict, and firing rate patterns change dramatically under conditions in which pitch percepts remain invariant; (7) cochleotopic organization of frequency-selective neurons bears little if any relevance to perceptual acuity and pitch constancy; and (8) simple temporal codes for pitch capable of accounting for pitches higher than a few hundred hertz have not been found in the auditory cortex. The cortical code for pitch is therefore not likely to be a function of simple rate profiles or synchronous temporal patterns. Studies motivated by interest in the neurophysiology and neuroanatomy of music perception have helped correct longstanding misconceptions about the functional role of auditory cortex in frequency discrimination and pitch perception. Advancing knowledge about the neural coding of pitch is of fundamental importance to the future design of neurobionic therapies for hearing loss.

Classification of lower extremity movement patterns based on visual assessment: reliability and correlation with 2-dimensional video analysis.

CONTEXT: Abnormal movement patterns have been implicated in lower extremity injury. Reliable, valid, and easily implemented assessment methods are needed to examine existing musculoskeletal disorders and investigate predictive factors for lower extremity injury. OBJECTIVE: To determine the reliability of experienced and novice testers in making visual assessments of lower extremity movement patterns and to characterize the construct validity of the visual assessments. DESIGN: Cross-sectional study. SETTING: University athletic department and research laboratory. PATIENTS OR OTHER PARTICIPANTS: Convenience sample of 30 undergraduate and graduate students who regularly participate in athletics (age = 19.3 ± 4.5 years). Testers were 2 experienced physical therapists and 1 novice postdoctoral fellow (nonclinician). MAIN OUTCOME MEASURE(S): We took videos of 30 athletes performing the single-legged squat. Three testers observed the videos on 2 occasions and classified the lower extremity movement as dynamic valgus, no change, or dynamic varus. The classification was based on the estimated change in frontal-plane projection angle (FPPA) of the knee from single-legged stance to maximum single-legged squat depth. The actual FPPA change was measured quantitatively. We used percentage agreement and weighted κ to examine tester reliability and to determine construct validity of the visual assessment. RESULTS: The κ values for intratester and intertester reliability ranged from 0.75 to 0.90, indicating substantial to excellent reliability. Percentage agreement between the visual assessment and the quantitative FPPA change category was 90%, with a κ value of 0.85. CONCLUSIONS: Visual assessments were made reliably by experienced and novice testers. Additionally, movement-pattern categories based on visual assessments were in excellent agreement with objective methods to measure FPPA change. Therefore, visual assessments can be used in the clinic to assess movement patterns associated with musculoskeletal disorders and in large epidemiologic studies to assess the association between lower extremity movement patterns and musculoskeletal injury.

Dissociation of detection and discrimination of pure tones following bilateral lesions of auditory cortex.

It is well known that damage to the peripheral auditory system causes deficits in tone detection as well as pitch and loudness perception across a wide range of frequencies. However, the extent to which to which the auditory cortex plays a critical role in these basic aspects of spectral processing, especially with regard to speech, music, and environmental sound perception, remains unclear. Recent experiments indicate that primary auditory cortex is necessary for the normally-high perceptual acuity exhibited by humans in pure-tone frequency discrimination. The present study assessed whether the auditory cortex plays a similar role in the intensity domain and contrasted its contribution to sensory versus discriminative aspects of intensity processing. We measured intensity thresholds for pure-tone detection and pure-tone loudness discrimination in a population of healthy adults and a middle-aged man with complete or near-complete lesions of the auditory cortex bilaterally. Detection thresholds in his left and right ears were 16 and 7 dB HL, respectively, within clinically-defined normal limits. In contrast, the intensity threshold for monaural loudness discrimination at 1 kHz was 6.5 ± 2.1 dB in the left ear and 6.5 ± 1.9 dB in the right ear at 40 dB sensation level, well above the means of the control population (left ear: 1.6 ± 0.22 dB; right ear: 1.7 ± 0.19 dB). The results indicate that auditory cortex lowers just-noticeable differences for loudness discrimination by approximately 5 dB but is not necessary for tone detection in quiet. Previous human and Old-world monkey experiments employing lesion-effect, neurophysiology, and neuroimaging methods to investigate the role of auditory cortex in intensity processing are reviewed.

Rating leniency and halo in multisource feedback ratings: testing cultural assumptions of power distance and individualism-collectivism.

This study extends multisource feedback research by assessing the effects of rater source and raters' cultural value orientations on rating bias (leniency and halo). Using a motivational perspective of performance appraisal, the authors posit that subordinate raters followed by peers will exhibit more rating bias than superiors. More important, given that multisource feedback systems were premised on low power distance and individualistic cultural assumptions, the authors expect raters' power distance and individualism-collectivism orientations to moderate the effects of rater source on rating bias. Hierarchical linear modeling on data collected from 1,447 superiors, peers, and subordinates who provided developmental feedback to 172 military officers show that (a) subordinates exhibit the most rating leniency, followed by peers and superiors; (b) subordinates demonstrate more halo than superiors and peers, whereas superiors and peers do not differ; (c) the effects of power distance on leniency and halo are strongest for subordinates than for peers and superiors; (d) the effects of collectivism on leniency were stronger for subordinates and peers than for superiors; effects on halo were stronger for subordinates than superiors, but these effects did not differ for subordinates and peers. The present findings highlight the role of raters' cultural values in multisource feedback ratings.

Heats of vaporization of room temperature ionic liquids by tunable vacuum ultraviolet photoionization.

The heats of vaporization of the room temperature ionic liquids (RTILs) N-butyl-N-methylpyrrolidinium bistrifluorosulfonylimide, N-butyl-N-methylpyrrolidinium dicyanamide, and 1-butyl-3-methylimidazolium dicyanamide are determined using a heated effusive vapor source in conjunction with single photon ionization by a tunable vacuum ultraviolet synchrotron source. The relative gas phase ionic liquid vapor densities in the effusive beam are monitored by clearly distinguished dissociative photoionization processes via a time-of-flight mass spectrometer at a tunable vacuum ultraviolet beamline 9.0.2.3 (Chemical Dynamics Beamline) at the Advanced Light Source synchrotron facility. Resulting in relatively few assumptions, through the analysis of both parent cations and fragment cations, the heat of vaporization of N-butyl-N-methylpyrrolidinium bistrifluorosulfonylimide is determined to be DeltaH(vap)(298.15 K) = 195 +/- 19 kJ mol(-1). The observed heats of vaporization of 1-butyl-3-methylimidazolium dicyanamide (DeltaH(vap)(298.15 K) = 174 +/- 12 kJ mol(-1)) and N-butyl-N-methylpyrrolidinium dicyanamide (DeltaH(vap)(298.15 K) = 171 +/- 12 kJ mol(-1)) are consistent with reported experimental values using electron impact ionization. The tunable vacuum ultraviolet source has enabled accurate measurement of photoion appearance energies. These appearance energies are in good agreement with MP2 calculations for dissociative photoionization of the ion pair. These experimental heats of vaporization, photoion appearance energies, and ab initio calculations corroborate vaporization of these RTILs as intact cation-anion pairs.

Impaired processing of prosodic and musical patterns after right hemisphere damage.

The distinction between the processing of musical information and segmental speech information (i.e., consonants and vowels) has been much explored. In contrast, the relationship between the processing of music and prosodic speech information (e.g., intonation) has been largely ignored. We report an assessment of prosodic perception for an amateur musician, KB, who became amusic following a right-hemisphere stroke. Relative to matched controls, KB's segmental speech perception was preserved. However, KB was unable to discriminate pitch or rhythm patterns in linguistic or musical stimuli. He was also impaired on prosodic perception tasks (e.g., discriminating statements from questions). Results are discussed in terms of common neural mechanisms that may underlie the processing of some aspects of both music and speech prosody.