193.3 nm photodissociation of jet-cooled C2H5OH and C2H5OD has been studied by using the high-n Rydberg-atom time-of-flight technique. Isotope labeling study shows that the H-atom photofragment is produced preferentially from O–H bond fission upon ultraviolet excitation. Center-of-mass (c.m.) translational energy distribution of the H(D) atom and ethoxy radical photofragments has been obtained. Average c.m. product translational energy is large, with 〈ET〉=0.84Eavail for H+C2H5O and 〈ET〉=0.80Eavail for D+C2H5O, respectively. Maximum c.m. translational energy release yields an upper limit of the bond dissociation energy: D0(C2H5O–H)=103.7±0.5 kcal/mol and D0(C2H5O–D)=105.9±0.5 kcal/mol. The c.m. translational energy distribution of the C2H5O+H products reveals extensive C–O stretch and modest C–C–O bending excitation in the C2H5O radical, which can be rationalized by the geometric change in going from the parent molecule to the excited surface and then to the ethoxy radical product, and can be simulated by a simple Franck–Condon model. H-atom product angular distribution is anisotropic (with β≈−0.9), indicating a perpendicular electronic transition (à 1A″←X̃ 1A′) at 193.3 nm and a short excited-state lifetime (less than a rotational period). The obtained dynamic information implies that the C2H5O+H channel in 193.3 nm photodissociation of ethanol occurs via a prompt dissociation process and on a repulsive excited-state surface, and the ethoxy product vibrational distribution further reveals the detailed multidimensional features of this excited à 1A″ potential energy surface. Secondary photodissociation of the ethoxy radical has been observed and is briefly discussed.
The thermal decomposition of 1,3-butadiene, 1,3-butadiene-1,1,4,4-d(4), 1,2-butadiene, and 2-butyne at temperatures up to 1520 K was carried out by flash pyrolysis on a approximately 20 mus time scale. The reaction products were isolated by supersonic expansion and detected by single-photon (lambda = 118 nm) vacuum-ultraviolet time-of-flight mass spectrometry (VUV-TOFMS). Direct detection of CH(3) and C(3)H(3), as well as C(3)H(4), C(4)H(4), and C(4)H(5) products, provides insight into the initial steps involved in the complex pyrolysis of these C(4)H(6) species below T = 1500 K. The similar pyrolysis product distributions for the C(4)H(6) isomers on such a short time scale support the previously proposed mechanism of facile isomerization of these species. Isomerization of 1,3-butadiene to 1,2-butadiene and subsequent C-C bond fission of 1,2-butadiene to produce CH(3) and C(3)H(3) (propargyl) are most likely the primary initial radical production channel in the 1,3-butadiene pyrolysis.
The peroxy radical chemical amplification (PERCA) method is combined with cavity ringdown spectroscopy(CRDS) to detect peroxy radicals (HO2 and RO2). In PERCA, HO2 and RO2 are first converted to NO2 via reactions with NO, and the OH and RO coproducts are recycled back to HO2 in subsequent reactions with CO and O2; the chain reactions of HO2 are repeated and amplify the level of NO2. The amplified NO2 is then monitored by CRDS, a sensitive absorption technique. The PERCA-CRDS method is calibrated using a HO2 radical source (0.5-3 ppbv), which is generated by thermal decomposition of H2O2 vapor (permeated from 2% H2O2 solution through a porous Teflon tubing) up to 600 degrees C. Using a 2-m long 6.35-mm o.d. Teflon tubing as the flow reactor and 2.5 ppmv NO and 2.5-10% vol/vol CO, the PERCA amplification factor or chain length, Delta[NO2]/([HO2]+[RO2]), is determined to be 150 +/- 50 (90% confidence limit) in this study. The peroxy radical detection sensitivity by PERCA-CRDS is estimated to be approximately 10 pptv/60 s (3sigma). Ambient measurements of the peroxy radicals are carried out at Riverside, California in 2007 to demonstrate the PERCA-CRDS technique.
Predicting pre-disease state or tipping point just before irreversible deterioration of health is a difficult task. Edge-network analysis (ENA) with dynamic network biomarker (DNB) theory opens a new way to study this problem by exploring rich dynamical and high-dimensional information of omics data. Although theoretically ENA has the ability to identify the pre-disease state during the disease progression, it requires multiple samples for such prediction on each individual, which are generally not available in clinical practice, thus limiting its applications in personalized medicine. In this work to overcome this problem, we propose the individual-specific ENA (iENA) with DNB to identify the pre-disease state of each individual in a single-sample manner. In particular, iENA can identify individual-specific biomarkers for the disease prediction, in addition to the traditional disease diagnosis. To demonstrate the effectiveness, iENA was applied to the analysis on omics data of H3N2 cohorts and successfully detected early-warning signals of the influenza infection for each individual both on the occurred time and event in an accurate manner, which actually achieves the AUC larger than 0.9. iENA not only found the new individual-specific biomarkers but also recovered the common biomarkers of influenza infection reported from previous works. In addition, iENA also detected the critical stages of multiple cancers with significant edge-biomarkers, which were further validated by survival analysis on both TCGA data and other independent data.
Nitrous acid (HONO) plays an important role in the formation of hydroxyl radical and the nitrogen cycle in atmospheric chemistry. Cavity ring-down spectroscopy (CRDS) has been utilized for detection of gaseous HONO in the near-UV spectral region. At the maximum absorption wavelength (354.2 nm), HONO can be detected with a low limit of 5 parts per billion (ppb) in 15 s sampling time, while at a low absorption wavelength, with a high value of 10 parts per million (ppm). The CRDS technique has a large dynamic range of detection, with a good linearity of absorbance versus concentration. The detection sensitivity demonstrated in this study is in the range of the ambient HONO concentration (0.1−10 ppb), and it can be readily improved to a sub-ppb level with upgraded optics and longer cavity. Moreover, this high detection sensitivity is realized with a relatively compact setup (in ∼ meters) and with a short sampling time (in 15 s). CRDS renders a promising technique for real-time and absolute measurements of HONO in laboratory and ambient studies. Absorption spectrum and cross sections of HONO near 354 nm have also been examined.
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