King-Chuen Lin

Detection of iron species using inductively coupled plasma mass spectrometry under cold plasma temperature conditions

Under the conditions of low radio frequency (rf) power of 600 W and aerosol gas flow rate of 1.25–1.35 l/min, 56Fe (or 54Fe) ions can be detected from the isobaric interference of the ArO+ (or ArN+) matrix. Using this method, the detection limit of 56Fe can reach 16 ng/l (ppt), 60 times smaller than by normal plasma conditions at 1200 W rf power. The linear dynamic range of the analyte measurement extends to 1000 ng/ml (ppb).

Chemically Induced Fluorescence Switching of Carbon-Dots and Its Multiple Logic Gate Implementation

Investigations were carried out on the carbon-dots (C-dots) based fluorescent off - on (Fe3 + - S2O32−) and on - off (Zn2 + - PO43−) sensors for the detection of metal ions and anions. The sensor system exhibits excellent selectivity and sensitivity towards the detection of biologically important Fe3 + , Zn2 +  metal ions and S2O32−, PO43− anions. It was found that the functional group on the C-dots surface plays crucial role in metal ions and anions detection. Inspired by the sensing results, we demonstrate C-dots based molecular logic gates operation using metal ions and anions as the chemical input. Herein, YES, NOT, OR, XOR and IMPLICATION (IMP) logic gates were constructed based on the selection of metal ions and anions as inputs. This carbon-dots sensor can be utilized as various logic gates at the molecular level and it will show better applicability for the next generation of molecular logic gates. Their promising properties of C-dots may open up a new paradigm for establishing the chemical logic gates via fluorescent chemosensors.

The correlation between ion production and emission intensity in the laser-induced breakdown spectroscopy of liquid droplets

Abstract Laser-induced breakdown spectroscopy (LIBS) is applied to detect trace metals contained in liquids. The sample in the form of liquid droplets is generated with an electrospray ionization needle. The microdroplets are interacted with an impinging laser pulse approximately 2 mm downstream from the needle tip. A sequence of single-shot time-resolved LIB emission signals of Na, K and Al is detected, respectively. The LIB signal intensity integrated within a gate linearly correlates with the plasma current obtained simultaneously on a single-shot basis. The correlation plot exhibits a straight line, of which the slope increases with the sample concentration. Given the calibration curves and the focused cross-sections of the incident laser beam, the detection limits may be determined to be 0.63±0.02 (0.3 pg), 1.2±0.1 (0.5 pg), and 43±5 mg/l (21 pg) for Na, K, and Al, respectively. As compared to the correlation methods applied, our treatment is more straightforward to yield concentration information and the resulting detection limits are comparable to those reported previously. The dependence of the correlation plot on the adopted laser energy and wavelength is also characterized. The detection limits tend to be improved by applying a laser with larger pulse energy but shorter wavelengths.

Productions of I, I*, and C2H5 in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection.

Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I(*), and C(2)H(5) fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p (2)P(3/2))+C(2)H(5) (hotter internal states) and I(*)(5p (2)P(1/2))+C(2)H(5) (colder). In addition, a competitive ionization dissociation channel, C(2)H(5)I(+)+h nu-->C(2)H(5)+I(+), appears at the wavelengths <266 nm. The I/I(*) branching of the dissociation channels may be obtained directly from the C(2)H(5) (+) images, yielding the quantum yield of I(*) about 0.63-0.76, comparable to the case of CH(3)I. Anisotropy parameters (beta) determined for the I(*) channel remain at 1.9+/-0.1 over the wavelength range studied, indicating that the I(*) production should originate from the (3)Q(0) state. In contrast, the beta(I) values become smaller above 266 nm, comprising two components, direct excitation of (3)Q(1) and nonadiabatic transition between the (3)Q(0) and (1)Q(1) states. The curve crossing probabilities are determined to be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p (2)P(3/2)) production from the nonadiabatic contribution, as compared to the case of CH(3)I.

State‐selective reaction of excited potassium atom with hydrogen molecule. K*+H2→KH+H

By using a pump‐and‐probe technique, we have observed for the first time the product KH formed by reaction of K*(7S) with H2 in a single collision under bulk conditions. In contrast, no detectable laser‐induced fluorescence (LIF) signal of KH was detected as the K*(7S) was replaced by the K*(5D), a state having 88 cm−1 less energy. These experiments demonstrate for the first time the possibility for an alkali atom to undergo with the H2 molecule a state‐selective reaction. This reaction can be satisfactorily understood in terms of the harpoon mechanism. Measurements of the temperature dependence of the rate constant confirm the proposed mechanism.

Molecular elimination of Br2 in 248 nm photolysis of bromoform probed by using cavity ring-down absorption spectroscopy

By using cavity ring-down spectroscopy technique, we have observed the channel leading to Br(2) molecular elimination following photodissociation of bromoform at 248 nm. A tunable laser beam, which is crossed perpendicular to the photolysis laser beam in a ring-down cell, is used to probe the Br(2) fragment in the B(3)Pi(ou)(+)-X(1)Sigma(g)(+) transition using the range 515-524 nm. The ring-down time lasts 500 ns, so the rotational population of the Br(2) fragment may not be nascent nature, but its vibrational population should be. The vibrational population ratio of Br(2)(upsilon=1)/Br(2)(upsilon=0)=0.8+/-0.2 implies that the fragmented Br(2) is vibrationally hot. The quantum yield of the molecular elimination reaction is 0.23+/-0.05, consistent with the values of 0.26 and 0.16 reported in 234 and 267 nm photolysis of bromoform, respectively, using velocity ion imaging. A plausible photodissociation pathway is proposed, based upon this work and ab initio calculations. The A(1)A(2), B(1)E, and C(1)A(1) singlet states of bromoform are probably excited at 248 nm. These excited states may couple to the high vibrational levels of the ground state X(1)A(1) via internal conversion. This vibrationally excited bromoform readily surpasses a reaction barrier 389.6 kJ/mol prior to decomposition. The transition state structure tends to correlate with vibrationally hot Br(2). Dissociation after internal conversion of the excited states to vibrationally excited ground state should result in a large fraction of the available energy to be partitioned in vibrational states of the fragments. The observed vibrationally hot Br(2) fragment seems to favor the dissociation pathway from high vibrational levels of the ground state. Nevertheless, the other reaction channel leading to a direct impulsive dissociation from the excited states cannot be excluded.

Temperature effect on nascent rotational state distribution of product MgH in reaction of Mg(3s3p1P1)+H2→MgH+H

A pump‐and‐probe technique is utilized to yield a population distribution over the rotational quantum states of the nascent product MgH in the reaction of Mg(1P1) and H2. The resulting normalized profile of the MgH bimodal distribution at 693 K coincides with that at 733 K, as well as with the results obtained at 380 K by Breckenridge and co‐workers. This temperature dependence demonstrates that the bimodality actually results from the insertive reaction alone. This conclusion is consistent with the isotopic effect.

Determination of lanthanides in rock samples by inductively coupled plasma mass spectrometry using thorium as oxide and hydroxide correction standard

Abstract Determination of lanthanides by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using modified mathematical correction method has been studied. Normally, the ICP-MS analysis of middle and heavier lanthanides becomes difficult by severe spectroscopic overlap of M+, MO+ or MOH+ ions from lighter lanthanides and Ba. A correction method based on a single element oxide yield measurement, is a simple approach to correct for the above spectroscopic overlaps. But the uncertainty in the oxide and hydroxide yields measurement of lanthanides and barium over a long period of time can lead to inaccurate results even under fixed plasma conditions. To correct this, thorium was adopted as an oxide and hydroxide correction standard. Using a ratio of lanthanide oxide yield to thorium oxide yield, the lanthanide correction factors (LCF) were established and incorporated in the mathematical correction scheme. The same factors were also established for hydroxide correction. The proposed modified correction scheme was applied to the determination of lanthanides by ICP-MS from the USGS Standard Rock samples AGV-1 and G-2. The results are in good agreement with the reported values. The method also proved to be useful in isotopic ratio measurement of lanthanides having severe isobaric overlaps.

Reaction pathway, energy barrier, and rotational state distribution for Li (2 2PJ)+H2→LiH (X 1Σ+)+H

By using a pump-probe technique, we have observed the nascent rotational population distribution of LiH (v=0) in the Li (2 2PJ) with a H2 reaction, which is endothermic by 1680 cm−1. The LiH (v=0) distribution yields a single rotational temperature at ∼770 K, but the population in the v=1 level is not detectable. According to the potential energy surface (PES) calculations, the insertion mechanism in (near) C2v collision geometry is favored. The Li (2 2PJ)–H2 collision is initially along the 2A′ surface in the entrance channel and then diabatically couples to the ground 1A′ surface, from which the products are formed. From the temperature dependence measurement, the activation energy is evaluated to be 1280±46 cm−1, indicating that the energy required for the occurrence of the reaction is approximately the endothermicity. As Li is excited to higher states (3 2S or 3 2P), we cannot detect any LiH product. From a theoretical point of view, the 4A′ surface, correlating with the Li 3 2S state, may feasibly co...

Species-Selected Mass-Analyzed Threshold Ionization Spectra of m -Fluoroaniline Cation

Two-color resonant, two-photon mass-analyzed threshold ionization (MATI) spectroscopy was used to probe the ionic properties of m-fluoroaniline (MFA). The species selection from a mixture was achieved by tuning the frequency of the excitation laser to a specific intermediate level of MFA for the successive excitation, followed by pulsed field ionization. The MATI spectra were recorded by ionizing via the 00 vibrationless and the 41, 151, and 9b1 vibrational levels in the S1 state. The adiabatic ionization energy of MFA was determined to be 64 159 ± 5 cm−1 (7.9542 ± 0.0006 eV). Analysis of the spectral features shows that the active modes of the ion are closely related to the specified vibrations of the neutral. These findings indicate that the geometry of the ion is quite similar to that of the neutral in the S1 state.