K. Gulyuz

Hybrid quadrupole mass filter/quadrupole ion trap/time-of-flight-mass spectrometer for infrared multiple photon dissociation spectroscopy of mass-selected ions

We present a laboratory-constructed mass spectrometer optimized for recording infrared multiple photon dissociation (IRMPD) spectra of mass-selected ions using a benchtop tunable infrared optical parametric oscillator∕amplifier (OPO∕A). The instrument is equipped with two ionization sources, an electrospray ionization source, as well as an electron ionization source for troubleshooting. This hybrid mass spectrometer is composed of a quadrupole mass filter for mass selection, a reduced pressure (∼10(-5) Torr) quadrupole ion trap (QIT) for OPO irradiation, and a reflectron time-of-flight drift tube for detecting the remaining precursor and photofragment ions. A helium gas pulse is introduced into the QIT to temporarily increase the pressure and hence enhance the trapping efficiency of axially injected ions. After a brief pump-down delay, the compact ion cloud is subjected to the focused output from the continuous wave OPO. In a recent study, we implemented this setup in the study of protonated tryptophan, TrpH(+), as well as collision-induced dissociation products of this protonated amino acid [W. K. Mino, Jr., K. Gulyuz, D. Wang, C. N. Stedwell, and N. C. Polfer, J. Phys. Chem. Lett. 2, 299 (2011)]. Here, we give a more detailed account on the figures of merit of such IRMPD experiments. The appreciable photodissociation yields in these measurements demonstrate that IRMPD spectroscopy of covalently bound ions can be routinely carried out using benchtop OPO setups.

Crown Complexation of Protonated Amino Acids: Influence on IRMPD Spectra

We report infrared multiple photon dissociation (IRMPD) spectra for a series of crown-adducted, protonated amino acids, generated by electrospray ionization. The tight chelation of 18-crown-6 on the protonated NH(3)(+) moiety results in a considerable red shift of the NH(3)(+) stretch modes, notably the antisymmetric NH(3)(+) stretch. This is rationalized by a distortion of the NH(3)(+) normal mode potential energy surface, as verified by quantum chemical calculations. On the other hand, the local oscillator modes, such as the carboxylic acid OH stretch, indole NH stretch, and phenol OH stretches, remain well-resolved and are subject to minor and predictable blue shifts of 5-15 cm(-1). Other chemically diagnostic modes, such as the guanidine NH stretch and alcohol OH stretches, also have discernible band positions. Crucially, some of these diagnostic band positions have little to no overlap with one another and can hence be readily distinguished. In addition, the complexes are often found to efficiently photodissociate by neutral loss of 18-crown-6, particularly for higher-basicity amino acids. This in principle opens the door on multiplexing the IRMPD experiment, where the IR spectra of multiple precursors are recorded simultaneously.

Screening for phosphorylated and nonphosphorylated peptides by infrared photodissociation spectroscopy

We present an infrared laser-based mass spectrometric strategy to differentiate peptides that are phosphorylated (i.e., containing pS, pT, or pY) from those that are nonphosphorylated (i.e., containing S, T, or Y), and those peptides that have none of these moieties (i.e., containing neither pS, pT, pY nor S, T, Y). This is demonstrated for a series of tripeptides and for two larger octapeptides, showing that the diagnostic phosphate OH stretch (indicative for pS, pT, or pY) can be distinguished from the alcohol OH stretch (indicative for S, T, or Y). In addition, the infrared multiple photon dissociation (IRMPD) spectra of multiple peptide analytes are recorded simultaneously in a multiplexed fashion. This is achieved by complexing each peptide precursor with a noncovalently bound 18-crown-6 ether, which is detached upon resonant infrared photon absorption.

Polarization and relaxation of ^209Rn

The study of the nuclear polarization of radon is motivated by the expected large enhancement of sensitivity to a CP-violating electric dipole moment (EDM) in isotopes with octupole deformation or vibrational strength. In preparation for EDM measurements, the polarization of radon by spin exchange with laser-polarized alkali metals is studied. The measurement of the alignment of 209Rn using HPGe detectors to observe the resulting anisotropy in the 337 and 745 keV gamma rays emitted following electron-capture decay of 209Rn to 209At is demonstrated. Radon is polarized via spin-exchange collisions with rubidium atoms in an uncoated Pyrex optical pumping cell. Anisotropy measurements at several temperatures are used to study polarization and relaxation.

High Precision Determination of the β Decay Q(EC) Value of (11)C and Implications on the Tests of the Standard Model.

We report the determination of the Q(EC) value of the mirror transition of (11)C by measuring the atomic masses of (11)C and (11)B using Penning trap mass spectrometry. More than an order of magnitude improvement in precision is achieved as compared to the 2012 Atomic Mass Evaluation (Ame2012) [Chin. Phys. C 36, 1603 (2012)]. This leads to a factor of 3 improvement in the calculated Ft value. Using the new value, Q(EC)=1981.690(61)  keV, the uncertainty on Ft is no longer dominated by the uncertainty on the Q(EC) value. Based on this measurement, we provide an updated estimate of the Gamow-Teller to Fermi mixing ratio and standard model values of the correlation coefficients.

Collinear laser spectroscopy of francium using online rubidium vapor neutralization and amplitude modulated lasers

Performing collinear laser spectroscopy on low intensity radioactive beams requires sensitive detection techniques. We explain our apparatus to detect atomic resonances in neutralized (208-210)Fr ion beams at beam energies of 5 keV and intensities of 10(5) s(-1). Efficient neutralization (> or = 80%) is accomplished by passing the beam through a dense Rb vapor. Increased detection efficiency is achieved by amplitude modulating the exciting laser to decrease the scattered light background, allowing fluorescence detection only when the laser is near its minimum in the modulation cycle. Using this technique in a collinear geometry we achieve a background reduction by a factor of 180 and a signal-to-noise increase of 2.2, with the lifetime of the atomic state playing a role in the efficiency of this process. Such laser modulation will also produce sidebands on the atomic spectra which we illustrate.

Precision mass measurements of neutron-rich Co isotopes beyond N=40

The region near Z=28, N=40 is a subject of great interest for nuclear structure studies due to spectroscopic signatures in

Francium developments at stony brook

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Gas-Phase Structure and Dissociation Chemistry of Protonated Tryptophan Elucidated by Infrared Multiple-Photon Dissociation Spectroscopy

Ni suggesting a subshell closure at N=40. Trends in nuclear masses and their derivatives provide a complementary approach to shell structure investigations via separation energies. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N > 40 along the iron and cobalt chains. Here we present the first Penning trap measurements of

Diagnostic NH and OH vibrations for oxazolone and diketopiperazine structures: b2 from protonated triglycine.

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