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M C McCarthy

Publications and source records attributed to M C McCarthy.

At least 19 recordsLinked to original sources
PubMed2006

Detection of low-frequency lambda-doublet transitions of the free 12CH and 13CH radicals.

By Fourier transform microwave spectroscopy, lambda-doubling transitions of (12)CH and (13)CH in the lowest rotational levels of the X(2) product operator(1/2) ground state have been directly detected, which has not been done previously. For both radicals, hyperfine-split lines have been measured to an accuracy of better than 1 ppm between 3 and 15 GHz, an improvement of at least 2 orders of magnitude over previous laboratory data. The measured frequencies have been combined with all previous data for CH and (13)CH in the v = 0 level of the X(2) product operator electronic state to determine improved hyperfine parameters. The production of CH from various gases also has been studied and, with methanol, the yield of CH relative to OH. Astronomical studies of CH in higher rotational levels and (13)CH can now be undertaken on the basis of the present work.

Astronomical Phenomena↗
PubMed2006

Monobridged Si2H4.

The rotational spectrum of a new monobridged isomer of Si(2)H(4), denoted here as H(2)Si(H)SiH, has been detected by Fourier transform microwave spectroscopy of a supersonic molecular beam through the discharge products of silane. On the basis of high-level coupled cluster theory, this isomer is calculated to lie only 7 kcalmol above disilene (H(2)SiSiH(2)), the most stable isomeric arrangement of Si(2)H(4), and to be fairly polar, with a calculated dipole moment of mu = 1.14 D. The rotational spectrum of H(2)Si(H)SiH exhibits closely spaced line doubling, characteristic of a molecule undergoing high-frequency inversion. Transition state calculations indicate that inversion probably occurs in two steps: migration of the bridged hydrogen atom to form silylsilylene, H(3)SiSiH, and then internal rotation of the SiH(3) group, followed by the reverse process. The potential energy surface for this type of inversion is quite shallow, with a barrier height of only 2-3 kcalmol. Searches for the rotational lines of silylsilylene, calculated to be of comparable stability to H(2)Si(H)SiH but about five times less polar (mu = 0.23 D), have also been undertaken, so far without success, even though strong lines of H(2)Si(H)SiH have been detected. The favorable energetics and high polarity of monobridged Si(2)H(4) with respect to either disilene or silylsilylene make it a plausible candidate for radioastronomical detection in sources such as IRC + 10216, where comparably large silicon molecules such as SiS, SiC(3), and SiC(4) have already been discovered.

Journal Article↗
PubMed2005

Rotational spectra of the carbon-chain radicals HC5O, HC6O, and HC7O.

Three new free carbon-chain radicals, HC5O, HC6O, and HC7O, and their deuterated isotopic species have been observed by Fourier transform microwave spectroscopy of a supersonic molecular beam. In contrast to the shorter HCnO radicals, these all have linear heavy-atom backbones and 2Pi electronic ground states. Like the isovalent HCnS radicals, the ground states of the HCnO radicals alternate with odd and even numbers of carbon atoms: those of HC5O and HC7O are 2Pi1/2 and that of HC6O is 2Pi3/2. From frequency measurements between 6 and 26 GHz, the rotational constant B, the centrifugal distortion constant D, and the lambda-type doubling and magnetic hyperfine constants have been determined to high precision for each chain. Predicted properties from coupled-cluster calculations are also reported for chains up to HC9O. The production of HCnO radicals for n even was highly favored when O2 was used as the source of oxygen, but those with n odd were best produced with CO.

Journal Article↗
PubMed2005

Rotational spectroscopy and equilibrium structures of S3 and S4.

The sulfur molecules thiozone S3 and tetrasulfur S4 have been observed in a supersonic molecular beam in the centimeter-wave band by Fourier transform microwave spectroscopy, and in the millimeter- and submillimeter-wave bands in a low-pressure glow discharge. For S3 over 150 rotational transitions between 10 and 458 GHz were measured, and for S4 a comparable number between 6 and 271 GHz. The spectrum of S3 is reproduced to within the measurement uncertainties by an asymmetric top Hamiltonian with three rotational and 12 centrifugal distortion constants; ten distortion constants, but an additional term to account for very small level shifts caused by interchange tunneling, are required to reproduce to comparable accuracy the spectrum of S4. Empirical equilibrium (r(e)(emp)) structures of S3 and S4 were derived from experimental rotational constants of the normal and sulfur-34 species and vibrational corrections from coupled-cluster theory calculations. Quantum chemical calculations show that interchange tunneling occurs because S4 automerizes through a transition state with D2h symmetry which lies about 500 cm(-1) above the two equivalent C2upsilon minima on the potential energy surface.

Journal Article↗
PubMed2005

Fourier transform microwave spectroscopy of vinyldiacetylene, vinyltriacetylene, and vinylcyanodiacetylene.

The rotational spectra of the three carbon chain molecules vinyldiacetylene (hex-1-ene-3,5-diyne, C(6)H(4)), vinyltriacetylene (oct-1-ene-3,5,7-triyne, C8H4), and its cyano analog vinylcyanodiacetylene (1-cyanohex-5-ene-1,3-diyne, C7H3N) have been observed for the first time by Fourier transform microwave spectroscopy of a supersonic molecular beam. The molecules were observed as products of an electrical discharge through selected precursor mixtures: ethylene/diacetylene and vinylacetylene/diacetylene for the pure hydrocarbon molecules and vinylacetylene/cyanoacetylene for vinylcyanodiacetylene. The measurements yield precise sets of rotational constants that compare very well with theoretical constants obtained by quantum chemical calculations at the B3LYP/cc-pVTZ level of theory. Since these three carbon chains are similar in structure and composition to known astronomical molecules and because of their significant polarity, all three are candidates for radio astronomical detection.

Journal Article↗
PubMed2005

Rotational spectrum and carbon-13 hyperfine structure of the C3H, C5H, C6H, and C7H radicals.

By means of Fourier transform microwave spectroscopy of a supersonic molecular beam, we have detected the singly substituted carbon-13 isotopic species of C(5)H, C(6)H, and C(7)H. Hyperfine structure in the rotational transitions of the lowest-energy fine structure component ((2)Pi(12) for C(5)H and C(7)H, and (2)Pi(32) for C(6)H) of each species was measured between 6 and 22 GHz, and precise rotational, centrifugal distortion, Lambda-doubling, and (13)C hyperfine coupling constants were determined. In addition, resolved hyperfine structure in the lowest rotational transition (J = 32-->12) of the three (13)C isotopic species of C(3)H was measured by the same technique. By combining the centimeter-wave measurements here with previous millimeter-wave data, a complete set of (13)C hyperfine coupling constants were derived to high precision for each isotopic species. Experimental structures (r(0)) have been determined for C(5)H and the two longer carbon-chain radicals, and these are found to be in good agreement with the predictions of high-level coupled-cluster calculations. C(3)H, C(5)H, and C(7)H exhibit a clear alternation in the magnitude and sign of the (13)C hyperfine coupling constants along the carbon-chain backbone. Because the electron spin density is nominally zero at the central carbon atom of C(3)H, C(5)H, and C(7)H, and at alternating sets of carbon atoms of C(5)H and C(7)H, owing to spin polarization, almost all of the (13)C coupling constants at these atoms are small in magnitude and negative in sign. Spin-polarization effects are known to be important for the Fermi-contact (b(F)) term, but prior to the work here they have generally been neglected for the hyperfine terms a, c, and d.

Journal Article↗
PubMed2005

Laser spectroscopy of Si3C.

The C 1B1<--X 1A1 band system of the potential interstellar species Si3C has been recorded in a silane/acetylene discharge by resonant two-color two-photon ionization spectroscopy. The origin band is located near 24,925 cm-1 (3.09 eV). Several other features in the spectrum are assigned to progressions in the Si-Si stretching modes as well as to sequence and hot band transitions. The assignment was facilitated by ab initio calculations, which also indicate that this is the strongest electronic transition of Si3C in the visible region of the spectrum. Features in the spectrum are broadened considerably (ca. 10 cm-1), and suggest an excited state lifetime of a few picoseconds. Possible reasons for the short-lived nature of the excited state are discussed.

Journal Article↗
PubMed2004

Tetrasulfur, S4: rotational spectrum, interchange tunneling, and geometrical structure.

The rotational spectrum of S4 has been observed for the first time in an electrical discharge through sulfur vapor. Two techniques have been used: Fourier transform microwave spectroscopy and long-path millimeter-wave absorption spectroscopy. Small, but systematic shifts of the measured transition frequencies of the normal isotopic species indicate that S4 has C2v symmetry but with a low-lying transition state of D2h symmetry, yielding interchange tunneling at 14.1(2) kHz in its ground vibrational state. From the rotational constants of the normal and the single 34S isotopic species, an experimental (r0) structure has been derived: S4 is a singlet planar trapezoid with a terminal bond length of 1.899(7) A, a central bond of 2.173(32) A, and an S-S-S angle of 103.9(8) degrees. Like thiozone (S3), S4 is a candidate for detection in the atmosphere of the Jovian moon Io and in other astronomical sources.

Journal Article↗
PubMed2003

Mono- and dibridged isomers of Si2H3 and Si2H4: the true ground state global minima. Theory and experiment in concert.

Highly correlated ab initio coupled-cluster theories (e.g., CCSD(T), CCSDT) were applied on the ground electronic states of Si(2)H(3) and Si(2)H(4), with substantive basis sets. A total of 10 isomers, which include mono- and dibridged structures, were investigated. Scalar relativistic corrections and zero-point vibrational energy corrections were included to predict reliable energetics. For Si(2)H(3), we predict an unanticipated monobridged H(2)Si-H-Si-like structure (C(s), (2)A'') to be the lowest energy isomer, in constrast to previous studies which concluded that either H(3)Si-Si (C(s), (2)A'') or near-planar H(2)Si-SiH (C(1), (2)A) is the global minimum. Our results confirm that the disilene isomer, H(2)Si-SiH(2), is the lowest energy isomer for Si(2)H(4) and that it has a trans-bent structure (C(2)(h), (1)A(g)). In addition to the much studied silylsilylene, H(3)Si-SiH, we also find that a new monobridged isomer H(2)Si-H-SiH (C(1), (1)A, designated 2c) is a minimum on the potential energy surface and that it has comparable stability; both isomers are predicted to lie about 7 kcal/mol above disilene. By means of Fourier transform microwave spectroscopy of a supersonic molecular beam, the rotational spectrum of this novel Si(2)H(4) isomer has recently been measured in the laboratory, as has that of the planar H(2)Si-SiH radical. Harmonic vibrational frequencies as well as infrared intensities of all 10 isomers were determined at the cc-pVTZ CCSD(T) level.

Journal Article↗
PubMed2003

Rotational spectrum and structure of Si3.

The rotational spectrum of a pure silicon cluster, the Si3 trimer, has been observed for the first time. From the rotational constants of the normal and the 29Si and 30Si isotopic species, a precise geometrical structure has been derived: the trimer is an isosceles triangle with a bond to the apex Si of length 2.177(1) A and an apex angle of 78.10(3) degrees. The substantial inertial defect and fairly large centrifugal distortion suggest that the molecule possesses a shallow bending potential. Si3 is a good candidate for astronomical detection because radio lines of comparably massive silicon molecules (e.g., SiC2, SiC4, and SiS) are readily observed in at least one astronomical source. The rotational spectra of Si6, Si9, and even larger polar silicon clusters may be detectable with the present technique, as well as similar germanium clusters.

Journal Article↗
PubMed2001

Carbon chains and rings in the laboratory and in space.

Seventy-seven reactive organic molecules of astrophysical interest have been identified in a supersonic molecular beam, 73 in the radio band by Fourier-transform microwave spectroscopy, four in the optical by laser cavity ringdown spectroscopy. Most are linear carbon chains, but six consist of carbon chains attached to the compact, highly polar C3 ring, and two are rhomboidal cyclic configurations of SiC3. The laboratory astrophysics of the radio molecules is complete for the time being, in the sense that essentially all the rotational transitions of current interest to radio astronomy (including hyperfine structure when present) can now be calculated to a small fraction of 1 km s(-1) in equivalent radial velocity; six of the radio molecules have already been detected in space on the basis of the present data. The FTM spectrometer employed in this work is far from fundamental limits of sensitivity, so many more molecules can probably be found by refinements of present techniques. The density of reactive molecules in our supersonic beam is generally high by the standards of laser spectroscopy, and many of the radio molecules probably have detectable optical transitions which we are attempting to find, largely motivated by the long-standing problem of the diffuse interstellar bands. Our most interesting result to date is the detection of a fairly strong molecular band at 443 nm in a benzene discharge, in exact coincidence with the strongest and best known interstellar band. Isotopic shifts measured with partially and totally deuterated benzene suggest that the carrier of the laboratory band is a hydrocarbon molecule with the elemental formula CnH5, with n most likely in the range 3-6.

Astronomical Phenomena↗
PubMed2001

Facial fractures in a level I trauma centre: the importance of protective devices and alcohol abuse.

Urban trauma centres have recently noted a shift in the causative mechanism of facial fractures away from motor vehicle crashes (MVC) to blunt assaults (BA). This study was conducted to examine the incidence and aetiology of facial fractures at our institution as well as the relationship with alcohol and protective device use. Trauma registry records of all patients admitted to a level I trauma centre from 1 January 1988 to 1 January 1999 were reviewed. There were 13594 trauma admissions during the 11-year period. Facial fractures were sustained by 1429 patients (10.5%) and this group forms the subject of this study. MVC was the predominant aetiology (59.9%) followed by BA (18.8%). Facial fractures were found in 9.5% of restrained MVC patients compared to 15.4% of unrestrained patients (P<0.00l). Non-helmeted motorcyclists were four times more likely to sustain facial fractures (4.3% vs. 18.4%) than helmeted patients (P<0.00l). 39.6% of patients in the MVC group were legally intoxicated compared to 73.5% in the BA group (P<0.00l). 45.4% of unrestrained patients with facial fractures were intoxicated compared to 11.8% of restrained MVC patients with facial fractures (P<0.001). MVC continue to be the primary aetiology of facial fractures in our trauma population. Protective devices decrease the incidence of facial fractures. Lack of protective device use and the consumption of alcohol correlate with sustaining facial fractures.

Accidents, Traffic↗
PubMed2000

Immunity to onchocerciasis: cells from putatively immune individuals produce enhanced levels of interleukin-5, gamma interferon, and granulocyte-macrophage colony-stimulating factor in response to Onchocerca volvulus larval and male worm antigens.

Antigen-specific interleukin-5 (IL-5), gamma interferon (IFN-gamma), and granulocyte-macrophage colony-stimulating factor (GM-CSF) responses in individuals living in an area of hyperendemicity for onchocerciasis in Cameroon were examined. The responses against antigens prepared from Onchocerca volvulus third-stage larvae (L3), molting L3 (mL3), and crude extract from adult males (M-OvAg) were compared to the responses against antigens from adult female worms and skin microfilariae. Cytokine responses for the putatively immune individuals (PI) and the infected individuals (INF) were compared. A differential cytokine profile of IL-5 (Th2 phenotype) and IFN-gamma (Th1 phenotype) was found in these individuals in response to the antigens. In both the PI and the INF, Th2 responses against all the antigens tested were dominant. However, in the PI group as a whole, there was an enhanced Th2 response against the larval antigens and the adult male and adult female antigens, and a Th1 response in a subgroup of the PI (27 to 54.5%) against L3, mL3, and M-OvAg antigens was present. While the PI produced significantly higher levels of GM-CSF against L3, mL3, and M-OvAg antigens than the INF, there was no difference in the GM-CSF responses of the groups against the other antigens. The present study indicated that, in comparison to the INF, the PI have distinct larva-specific and adult male-specific cytokine responses, thus supporting the premise that immunological studies of the PI would lead to the identification of immune mechanisms and the target genes that play a role in protective immunity.

Animals↗
PubMed1999

APACHE II and ISS scores as predictors of nosocomial infections in trauma patients.

BACKGROUND: Nosocomial infections affect more than 2 million patients annually in the United States at a cost of $4.5 billion. The aim of this study is to identify the role of the APACHE II score and the Injury Severity Scale (ISS) as independent predictors of nosocomial infections in trauma patients admitted to the intensive care unit (ICU). METHODS: A retrospective chart review of 113 trauma patients admitted to the ICU was conducted by an infectious disease physician. Demographic data and incidence of nosocomial infections were recorded. Multivariate logistic regression analysis was used to determine variables that are predictive of the occurrence of nosocomial infections. RESULTS: Presence or absence of intubation, ICU length of stay, APACHE II score, and ISS were related to the presence of infections; however, only the ICU length of stay was an independent predictor of a nosocomial infection, with an odds ratio of 1.81. By linear regression, 17% of the variance in the ICU duration of stay was a result of the APACHE II score in patients with a score >/=5. CONCLUSION: APACHE II score and ISS score were not good predictors of the incidence of nosocomial infections in trauma patients admitted to the ICU, but the APACHE II score has a modest correlation with the duration of stay in the ICU. A stratified cohort study could identify the subset of patients for which the APACHE II score predicts a prolonged stay in the ICU, thus an increased risk of infection.

APACHE↗
PubMed1999

Children's and parents' visual perception of physicians.

The purpose of this study is to evaluate the child's and parents' visual perception of physicians. To do this, 50 children and their parents were asked which physician they preferred, when shown eight pairs of photographs. Four characteristics were tested twice, white coat versus no white coat, smile versus stern face, cartoon posters versus no posters, and standing versus stooping. We found that both children and parents preferred the smiling physician and the physician with cartoon posters on the wall. Surprisingly 54% of children preferred the physician in the white coat, whereas only 35% of parents preferred the white coat. Sixty-eight percent of children also preferred the standing physician compared with only 41% of parents. There was little correlation between the parent's and child's answers. The results did not differ significantly with age, gender, or number of hospitalizations. In conclusion our study did not confirm the popular belief that children are afraid of physicians in white coats, although children did strongly prefer physicians who smiled and those with cartoon posters on the wall.

Adult↗
PubMed1999

Traditional criteria for observation of splenic trauma should be challenged.

Age less than 55 years, normal Glasgow Coma Score (GCS), and absence of hypotension are traditional criteria for the selection of adult patients with blunt splenic trauma for observation. The objective of this study is to challenge these criteria. Two hundred twelve patients who presented with blunt splenic injury between 1992 and 1997 were identified from the Trauma Registry at our Level I trauma center. The patients were divided into three groups: 100 patients (47%) were observed, 108 (51%) underwent immediate splenorrhaphy or splenectomy, and 4 (2%) failed observation. The three groups were compared by participants' ages, GCSs, and histories of hypotension. No statistical differences were noted between the successfully observed patients and those requiring immediate surgery with respect to these criteria. Of the 4 patients who failed observation, all were younger than 55 years, all had a GCS >12, and all were normotensive. Our findings suggest that traditional criteria used to select patients for splenic trauma observation are not absolute indicators and should be liberalized: patients can be successfully observed despite having criteria that, in the past, would have led to immediate operative intervention.

Blood Pressure↗