Transitions Of CS Research Articles

Reassessment of the Level of Theory Required for the Epoxidation of Ethylene with Dioxiranes

High level ab initio and CASSCF calculations on the epoxidation of ethylene with dioxirane (DO) and dimethydioxirane (DMDO) have been carried out to distinguish between a symmetrical versus an unsymmetrical spiro orientation of the dioxirane in the transition structure for oxygen atom transfer. The optimized C1 DO/ethylene unsymmetrical spiro CASSCF(12,12)/6-31G(d) transition structure is a first-order saddle point that is 5.5 kcal/mol lower in energy than the corresponding constrained Cs symmetrical approach (a second-order saddle point) after correction for dynamic correlation [CASSCF(MP2)]. However, a single-point energy correction at the BD(T)/6-311+G(d,p) level on these CASSCF geometries suggests that the C1 TS is only 0.6 kcal/mol lower in energy than an symmetrical spiro TS. Both the BD(T) correction to the CAS(8,8)/6-31+G(d,p) and RSPT2 energy correction on CAS(8,8)/6-31G(d) DO/ethylene structures slightly favors the Cs structures. BD(T)/6-311+G(d,p) single point calculations on the C1 and Cs transition structures optimized at the CCSD(T)/6-31G(d) level slightly favor the unsymmetrical TS. These combined data suggest that the potential energy surface for the approach of dioxirane to the CC of ethylene is very soft with the C1 transition structure being slightly favored. For DMDO epoxidation, we conclude that the approach of DMDO to a symmetrically substituted alkene should result in an essentially symmetrical transition structure.

Identifying Young Brown Dwarfs Using Gravity‐Sensitive Spectral Features

We report the initial results of the Brown Dwarf Spectroscopic Survey Gravity Project to study gravity sensitive features as indicators of youth in brown dwarfs. Low-resolution (R ~ 2000) J-band and optical (R ~ 1000) observations using NIRSPEC and LRIS at the W. M. Keck Observatory reveal transitions of TiO, VO, K I, Na I, Cs I, Rb I, CaH, and FeH. By comparing these features in late-type giants and in old field dwarfs, we show that they are sensitive to the gravity (g = GM/R2) of the object. Using low-gravity spectral signatures as age indicators, we observed and analyzed J-band and optical spectra of two young brown dwarfs, G196-3B (20-300 Myr) and KPNO Tau 4 (1-2 Myr) and two possible low-mass brown dwarfs in the σ Orionis cluster (3-7 Myr). We report the identification of the bands of TiO near 1.24 μm and the A-X band of VO near 1.18 μm together with extremely weak J-band lines of K I in KPNO Tau 4. This is the first detection of TiO and VO in the J band in a substellar-mass object. The optical spectrum of KPNO Tau 4 exhibits weak K I and Na I lines, weak absorption by CaH, and strong VO bands, also signatures of a lower gravity atmosphere. G196-3B shows absorption features in both wavelength regions, like those of KPNO Tau 4, suggesting that its age and mass are at the lower end of published estimates. Whereas σ Ori 51 appears to be consistent with a young substellar object, σ Ori 47 shows signatures of high gravity most closely resembling an old L1.5/L0 and cannot be a member of the σ Orionis cluster.

On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B

We have characterized the internal structure of two close-to-round starless cores in Taurus, L1498 and L1517B, setting constraints on the initial conditions of star formation and on models of core condensation. Our analysis is based on high angular resolution observations in at least two transitions of NH3, N2H+, CS, C34S, C18O, and C17O, together with maps of the 1.2 mm continuum. For both cores, we derive radial profiles of constant temperature and constant turbulence, and density distributions close to those of non-singular isothermal spheres. Using a Monte Carlo radiative transfer model, we derive abundance profiles for all species and find a pattern of strong chemical differentiation. NH3 has a higher abundance toward the core centers while N2H+ has a constant abundance over most of the cores. Both C18O and CS (and isotopomers) are strongly depleted in the core interiors, most likely due to their freeze out onto cold dust grains. Concerning the kinematics of the dense gas, we find (in addition to constant turbulence) a pattern of internal motions at the level of 0.05 km s−1. These motions seem correlated with asymmetries in the pattern of molecular depletion, and we interpret them as residuals of core contraction. Their distribution and size suggest that core formation happens in rather irregular manner. A comparison with supersonic turbulence models of core formation shows that our observed cores are much more quiescent than allowed by these models.

The Trumpler 14 photodissociation region in the Carina Nebula

We report the results of observations of the fine-structure emission lines (C ) 158 µ ma nd (O )6 3µm using FIFI on the Kuiper Airborne Observatory (KAO) and the Long Wavelength Spectrometer (LWS) on board ISO, towards the molecular cloud associated with the stellar cluster Trumpler 14 (Tr 14) in the Carina Nebula. These data are compared with selected CO and CS transitions obtained with the SEST as well as IRAS and MSX images to produce a detailed view of the morphology and the physical conditions prevailing in the photodissociation region (PDR) at the interface between the ionized gas and the molecular dust lane. The relative intensity distribution observed for the various tracers is consistent with the stratification expected for a molecular cloud seen edge-on and exposed to a radiation field of ≈10 4 G0, which is dominated by the most massive stars of Tr 14. The grain photoelectric heating efficiency, � , is estimated to be ≈5 × 10 −3 and is comparable to other galactic PDRs. The molecular gas has a complicated velocity structure with a high velocity dispersion resulting from the impact of the stellar winds arising from Tr 14. There is evidence of small-scale clumping with a very low volume filling factor. Despite the rich concentration of massive O stars in Tr 14 we find that the parameters of the PDR are much less-extreme than those of the Orion and M 17 massive star-forming regions.

Prospects for forbidden-transition spectroscopy and parity violation measurements using a beam of cold stable or radioactive atoms

Laser cooling and trapping offers the possibility of confining a sample of radioactive atoms in free space. Here, we address the question of how best to take advantage of cold atom properties to perform the observation of as highly forbidden a line as the 6S-7S Cs transition for achieving, in the longer term, Atomic Parity Violation measurements in radioactive alkali isotopes. Another point at issue is whether one might do better with stable, cold atoms than with thermal atoms. To compensate for the large drawback of the small number of atoms available in a trap, one must take advantage of their low velocity. To lengthen the time of interaction with the excitation laser, we suggest choosing a geometry where the laser beam exciting the transition is colinear to a slow, cold atomic beam, either extracted from a trap or prepared by Zeeman slowing. We also suggest a new observable physical quantity manifesting APV, which presents several advantages:specificity, efficiency of detection, possibility of direct calibration by a parity conserving quantity of a similar nature. It is well adapted to a configuration where the cold atomic beam passes through two regions of transverse, crossed electric fields, leading both to differential measurements and to strong reduction of the contributions from the M_1-Stark interference signals, potential sources of systematics in APV measurements. Our evaluation of signal to noise ratios shows that with available techniques, measurements of transition amplitudes, important as required tests of Atomic Theory should be possible in cesium 133 with a statistical precision of 1/1000 and probably also in Fr isotopes for production rates of 10^6 Fr atoms/s.

A theoretical study of the azide (N3) doublet states. A new route to tetraazatetrahedrane (N4): N+N3→N4

The potential energy surfaces for the low-lying doublet states of the azide radical (N3) have been computed at the complete active space self-consistent field (CASSCF) level with the CAS(15,12) active space. The cc-pVTZ and aug-cc-pVTZ basis sets have been employed throughout the present work. Energies, geometries and harmonic frequencies were determined for the N3 linear ground electronic state (2Πg), a stable C2v ring structure (2B1), and a Cs transition state (2A″) connecting the ring and linear structures. Other N3 (C2v) stationary points (2A2, B12, and A12) have been characterized, as well. The vertical excitation energies for the doublet excited states of the N3 linear (2Πg) and stable ring (2B1) isomers were calculated using CASSCF and multireference configuration interaction [MRCI-SD(Q)] methods. A new route to tetraazatetrahedrane [N4(Td)] has been proposed on the N4 singlet potential energy surface within Cs symmetry. MRCI-SD(Q) calculations predict that N4 (Td) can be formed from atomic nitrogen in the D2 state and N3 (C2v, B12) in a barrierless exothermic reaction. The energy difference (D0) is 135.4 kcal/mol at the MRCI-SD(Q) level.

Research Note On the frequency of the CS (J: 2$\rightarrow$1) and (J: 5$\rightarrow$4) transitions

While conducting high signal-to-noise ratio (SNR) observations of multiple transitions and different isotopomers of CS, SO and CO towards L183 (also known as L134N), we found that the CS ( J : 2$\rightarrow$1) line frequency established by Kuiper et al. ([CITE]) during observations towards L1498 was in disagreement with our observations. We have consequently repeated their observations towards that object, but in a slightly different manner by observing simultaneously the CS ( J : 2$\rightarrow$1) line at 98 GHz and the CCS ( J N : 8$_7\rightarrow7_6$) line at 94 GHz with the same telescope and the same receivers therefore eliminating the possibility of errors associated with either software or hardware. We found that our L183 data was best described with the standard frequency of 97 980.95 MHz. We also found a real difference in the velocity position of the CS and CCS peaks in L1498, but one only half that reported by Kuiper et al. ([CITE]). Most importantly, we have established that the L1498 cloud is not well-suited to set the CS ( J : 2$\rightarrow$1) frequency despite the exceptional narrowness of the lines. The CS ( J : 2$\rightarrow$1) line shape is far from Gaussian and suffers from strong effects, due either to large-scale movements (infall and/or rotation), or to self-absorption, or both. These results and other works (Lemme et al. [CITE]; Lee et al. [CITE]) have convinced us that these observations are consistent with the standard CS ( J : 2$\rightarrow$1) line frequency. We also checked the C 34 S ( J : 2$\rightarrow$1) and the CS ( J : 5$\rightarrow$4) transitions and found a major discrepancy for the latter with the JPL catalogue. Finally, CS transitions have been recently re-measured in the laboratory by Gottlieb et al. ([CITE]) with high precision and are found to be consistent with our interpretation.

Massive core parameters from spatially unresolved multi-line observations

We present observations of 15 massive cores in three different CS transitions from the FCRAO 14 m and the KOSMA 3 m telescope. We derive physical parameters of these cores using different approaches to the line radiative transfer problem. The local radiative transfer approximations fail to provide reliable values except for the column densities. A self-consistent explanation of the observed line profiles is only possible when taking density gradients and an internal turbulent structure of the cores into account. The observational data can be fitted by a spherically symmetric radiative transfer model including such gradients and a turbulent clumping. We find that the observed massive cores are approximately virialised with a clumpy density profile that decays with a radial exponent of about -1.6 down to a relatively sharp outer boundary. We show that a careful analysis of spatially unresolved multi-line observations using a physical radiative transfer model can provide values for physical parameters that could be obtained otherwise only by direct observations with much higher spatial resolution. This applies to all quantities directly affecting the line excitation, like the mass and size of dense cores. Information on the exact location or number of clumps, of course, always has to rely on high-resolution observations e.g. from interferometers.

Quiescent Giant Molecular Cloud Cores in the Galactic Center

We have used the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory (ISO) to map the far-infrared continuum emission (45-175 micrometer) toward several massive Giant Molecular Cloud (GMC) cores located near the Galactic center. The observed far-infrared and submillimeter spectral energy distributions imply low temperatures (approx. 15 - 22 K) for the bulk of the dust in all the sources, consistent with external heating by the diffuse ISRF and suggest that these GMCs do not harbor high- mass star-formation sites, in spite of their large molecular mass. Observations of FIR atomic fine structure lines of C(sub II) and O(sub I) indicate an ISRF enhancement of approx. 10(exp 3) in the region. Through continuum radiative transfer modeling we show that this radiation field strength is in agreement with the observed FIR and submillimeter spectral energy distributions, assuming primarily external heating of the dust with only limited internal luminosity (approx. 2 x 10(exp 5) solar luminosity). Spectroscopic observations of millimeter-wave transitions of H2CO, CS, and C-34S carried out with the Caltech Submillimeter Observatory (CSO) and the Institut de Radio Astronomie Millimetrique (IRAM) 30-meter telescope indicate a gas temperature of approx. 80 K, significantly higher than the dust temperatures, and density of approx. 1 x 10(exp 5)/cc in GCM0.25 + 0.01, the brightest submillimeter source in the region. We suggest that shocks caused by cloud collisions in the turbulent interstellar medium in the Galactic center region are responsible for heating the molecular gas. This conclusion is supported by the presence of wide-spread emission from molecules such as SiO, SO, and CH3OH, which are considered good shock tracers. We also suggest that the GMCs studied here are representative of the typical, pre-starforming cloud population in the Galactic center.

Millimeter Observations of Vibrationally Excited CS toward IRC +10216: A New Circumstellar Maser?

New observations of vibrationally excited CS in its v = 1 state have been conducted toward the circumstellar shell of IRC +10216 using the NRAO 12 m telescope and the CSO. The J = 3 → 2, 6 → 5, and 7 → 6 transitions in the v = 1 level at 146, 292, and 340 GHz have been detected toward this object, and the J = 2 → 1 and 5 → 4 lines were also reobserved. After accounting for contamination from other species, these CS transitions all exhibit line profiles that are narrower (ΔV1/2 ~ 10 km s-1) than those displayed by most molecules in IRC +10216, indicating an origin in the inner stellar envelope. The J = 3 → 2 line is particularly narrow (ΔV1/2 ~ 1-2 km s-1), and consists of two separate velocity components at VLSR ~ -26 and -22 km s-1. These characteristics are suggestive of weak maser action in this transition. The narrow line widths observed in the other transitions indicate a source size 05, which implies a CS column density in the v = 1 state of ~ 2-6 × 1016 cm-2. The ground-state (v = 0) column density is therefore on the order of 0.8-2 × 1018 cm-2 for Tvib = 500 K. The fractional abundance of CS relative to H2 is consequently f ~ 3-7 × 10-5 at ~ 14 R*. Such a high abundance close to the stellar photosphere is strong evidence that CS is a parent molecule in IRC +10216, as suggested by infrared studies of the v = 0 → 1 vibrational transition and interferometric observations.

Phonon instabilities in high-pressure bcc-fcc and the isostructural fcc-fcc phase transitions of Cs

The phonon instabilities of cesium related to its pressure-induced $\mathrm{bcc}\ensuremath{-}\mathrm{to}\ensuremath{-}{\mathrm{fcc}}^{(1)}\ensuremath{-}\mathrm{to}\ensuremath{-}{\mathrm{fcc}}^{(2)}$ phase transitions are studied using the density-functional perturbation theory. It is found that at low pressure, both the bcc and fcc Cs are dynamically stable, but fcc is thermodynamically metastable. The high-pressure phase transitions of Cs from bcc to ${\mathrm{fcc}}^{(1)}$ and from ${\mathrm{fcc}}^{(1)}$ to ${\mathrm{fcc}}^{(2)}$ are related to the phonon instabilities of the long-wavelength acoustic modes resulted from the negative tetragonal shear elastic constant ${C}^{\ensuremath{'}}=\frac{1}{2}{(C}_{11}\ensuremath{-}{C}_{12}).$ During the ${\mathrm{fcc}}^{(1)}\ensuremath{-}\mathrm{to}\ensuremath{-}{\mathrm{fcc}}^{(2)}$ phase transition, all the phonon modes become soft, making it the most striking feature of this isostructural phase transition.

A New Star-forming Core in the Norma Filamentary Dark Cloud

We report observations at millimeter and near-infrared wavelengths of the region near IRAS 16295-4452 seen toward the Sa 187 filamentary dark cloud in the southern constellation Norma. Observations in the main rotational transitions of CO, 13CO, CS, and HCN reveal a new dense cloud core associated with IRAS 16295-4452. The core has diameter ~0.3 pc and total mass ~35 M⊙. Near-infrared imaging of the same region shows that the reddest (H-K = 2.9) source seen in our images, which is undetected in the J image, is located about 11'' from IRAS 16295-4452 and is likely to be the near-infrared counterpart of the IRAS source. The millimeter observations reveal the presence of a molecular outflow with lobes extending in opposite directions from IRAS 16295-4452. The shape of the spectral energy distribution between 1.25 and 100 μm suggests that IRAS 16295-4452 is a Class I protostar with total luminosity about 35 L⊙.

Ab Initio Direct Dynamics Trajectory Study of the Cl- + CH3Cl SN2 Reaction at High Reagent Translational Energy

An ab initio (HF/3-21+G*) direct dynamics quasiclassical trajectory study was performed for the Cl- + CH3Cl SN2 reaction at a reagent relative translational energy of 100 kcal/mol. Initial conditions for the trajectories were averaged over the orientation of CH3Cl and the reaction dynamics studied versus collision impact parameter. The trajectories reacted by a backside attack mechanism and reaction by frontside attack was not observed. The calculated backside reaction cross reaction is 0.22−0.40 Å2 and approximately two to four times larger than the experimental value (J. Phys. Chem. A 1997, 101, 5969). The absence of reaction by frontside attack was investigated by initiating trajectories at the Cs transition state for the frontside attack mechanism. These trajectories formed Cl- + CH3Cl reactants with a large vibrational energy and low relative translational energy, which suggests extensive CH3Cl vibrational excitation is needed to access the frontside reaction pathway.

A Variation of Titanium-Induced Carbonyl Coupling – Synthesis and Conformations of Terfluorenyl

Reaction of fluorenone (4) with a low-valent titanium reagent generated from TiCl4 and Zn in THF in the presence of pyridine gave terfluorenyl (6) in 71% yield, bifluorenylidene (2), the conventional McMurry reaction product, in 2% yield, and additional reduction products. The reductive “trimerization” was rationalized in terms of an attack of the intermediate fluorenone dianion on bifluorenylidene. The molecular structure of a single crystal of 6 indicated an approximately C2 conformation, with a slightly twisted central ring, and two equally folded side moieties with dihedral angles of 58.1° and 58.0° between the central and side five-membered rings. The AM1 and PM3 calculations showed C2 global minima, similar to the conformation in the crystal. The calculated Cs transition state conformations were found to be 21.3 (AM1) and 19.9 (PM3) kcal/mol higher in energy than the global C2 minima. A 2D-NMR NOESY experiment on 6 supported the C2 (+sc,+sc) or C2 (–sc,–sc) conformation in solution.

High–Angular Resolution Millimeter‐Wave and Near‐Infrared Imaging of the Ultracompact HiiRegion G29.96−0.02

We present a high-angular resolution study of the cometary-shaped ultracompact H II region G29.96-0.02. We have obtained ~10'' angular-resolution millimeter-wave maps of the region in transitions of 13CO, C18O, CH3CN, CH3OH, and CS with the BIMA interferometer. We combine these data with complementary single-dish data of the 13CO, C18O, and CS lines taken with the FCRAO 14 meter telescope. These data are compared with near-infrared JHK-band images with ?09 angular resolution obtained with the Calar-Alto 3.5 m telescope. The 13CO data show emission extended over a 3 ? 2 pc region; however, the emission is strongly peaked near the head of the H II region. Strong CS, C18O, and CH3CN emissions peak near the same location. The CH3CN (J=6?5) emission peaks toward the hot core previously detected in VLA NH3(4, 4) observations, and we determine a kinetic temperature of 100 K in the core using a large velocity gradient analysis of the CH3CN (6?5) BIMA data and CH3CN/CH133CN (5?4) IRAM 30 m telescope data. We also find that the sharply peaked C18O, 13CO, and CS emission is indicative of a density gradient, with the peak density located in front of the head of the cometary H II region. We use our near-infrared data to search for sources embedded in the H II region and the adjacent cloud. In addition to the exciting star of the H II region, we identify a second star toward the head of the H II region with an extinction similar to that of the exciting star; this appears to be a second OB star in the H II region. Directly in front of the H II region we detect a highly reddened source, which is most likely a young star deeply embedded in the molecular gas. Furthermore, we find an enhanced density of sources with H-K >1 toward the molecular cloud and argue that these sources form an embedded cluster. Finally, we compare our results with current models of cometary shaped H II regions. Given the evidence that the G29.96 H II region exists in a gradient of molecular gas density that peaks in front of the head of the H II region, we favor the champagne flow model for this region. Comparing the measured densities, temperatures, and line widths of the ionized and molecular gas, we estimate the expansion speed of the H II region into the molecular core at 2-5 km s-1.

The Ionization Fraction in Dense Molecular Gas. II. Massive Cores

We present an observational and theoretical study of the ionization fraction in several massive cores located in regions that are currently forming stellar clusters. Maps of the emission from the J=1→0 transitions of C18O, DCO+, N2H+, and H13CO+, as well as the J=2→1 and 3→2 transitions of CS, were obtained for each core. Core densities are determined via a large velocity gradient analysis with values typically of ~105 cm-3. With the use of observations to constrain variables in the chemical calculations, we derive electron fractions for our overall sample of five cores directly associated with star formation and two apparently starless cores. The electron abundances are found to lie within a small range, -6.9 < log10xe < -7.3, and are consistent with previous work. We find no difference in the amount of ionization fraction between cores with and without associated star formation activity, nor is any difference found in electron abundances between the edge and center of the emission region. Thus our models are in agreement with the standard picture of cosmic rays as the primary source of ionization for molecular ions. With the addition of previously determined electron abundances for low-mass cores, and even more massive cores associated with O and B clusters, we systematically examine the ionization fraction as a function of star formation activity. This analysis demonstrates that the most massive sources stand out as having the lowest electron abundances (xe < 10-8).

The transition state of electrophilic aromatic substitution in the gas phase

Electrophilic aromatic substitution without solvent molecules is a one-step reaction. This is the result of an MP2/6-31+G** analysis of the benzene–HF–BF3 supermolecule. There is a qualitative agreement of this with an estimation given by Tomasi etal. in 1997 (Theoret. Chim. Acta, 1977, 45, 127). We report the structures of the BF3–HF–benzene complex and the degenerate Cs transition structures of the H exchange. However, considering the zero-point vibrational energies in order to get Δ‡H°(0), a broad transition state region including the C2v structure becomes evident. It demonstrates the large out-of-plane mobility of the reaction cycle. The cationic subunits of the zwitterionic transition structures resembles the well-known σ-complex structure. It is shown that the prolongation of the C–H bonds at the protonated C atom of benzene may lead to a small HCH angle and a transcyclic H···H bonding in the transition structure.

Molecular Abundance Enhancements in the Highly Collimated Bipolar Outflow BHR 71

We report observations of the J = 3 → 2 and J = 2 → 1 transitions of SiO and CS, the Jk = 3k → 2k and Jk = 2k → 1k transitions of CH3OH, and the J = 1 → 0 transition of HCO+, made with Swedish-ESO Submillimetre Telescope (SEST), toward the highly collimated bipolar outflow BHR 71. Broad wing emission was detected toward the outflow lobes in all the observed molecular lines. The shapes of the profiles are strikingly different from molecule to molecule. For CS and HCO+ the emission from the outflowing gas appears as a weak broad feature superposed upon a strong narrow emission from the quiescent ambient gas. For CH3OH the intensity of the broad emission feature is considerably stronger than that of the narrow component, whereas for SiO the broad feature completely dominates the emission spectra. The spatial distribution of the integrated wing emission is considerably extended and broadly similar in all the observed molecular transitions, showing well-separated blueshifted and redshifted lobes with FWHM angular sizes of 24 × 13 and 24 × 14, respectively. We find that the abundance of methanol and silicon monoxide in the outflow lobes is enhanced with respect to that of the ambient cloud by factors of up to ~40 and 350, respectively. The large enhancements of methanol and silicon monoxide in the outflow lobes are most likely due to the release from grains of ice mantles and Si-bearing species via shocks produced by the interaction between the outflow and dense ambient gas. On the other hand, we find that the abundance of HCO+ in the outflowing gas is smaller than that in the ambient gas by about a factor of 20, a decrease consistent with theoretical predictions of shock models.

Optical Investigation of Submonolayer Phase Transitions of Cs on GaAs(001)

Optical surface sensitive techniques can probe phase transitions of cesium overlayers on GaAs(001) of less than one monolayer thickness. For cesium deposition at near liquid nitrogen temperature, surface diffusion of cesium is prohibited and there form disordered two-dimensional clusters. We consider two types of transitions: (i) Annealing to room temperature enables surface diffusion and induces an ordering of the overlayer. This transition is revealed from the Reflectance Anisotropy (RA) spectrum since, for the gallium-rich surface, the optical anisotropy is due to localized states, sensitive to the local potential created by the cesium overlayer. (ii) The formation of metallic clusters is revealed by photoreflectance spectroscopy. It is also found that this metallic phase is metastable and is destroyed by annealing to room temperature.

Three‐dimensional Non‐LTE Radiative Transfer of CS in Clumpy Dense Cores

With a Monte Carlo radiative transfer code we have investigated excitation conditions of the CS molecule in dense cores and synthesized line profiles for several transitions of both CS and C34S. We took two kinds of models of the dense core: a clumpy and a smooth model. In the clumpy model, the core is composed of many small clumps, whose volume filling factor f is unity in the central region of r ≤ 0.2R and then declines as f r-1.5. However, H2 number density in the clump is kept constant and also independent of the clump position. The mean number density, nH2(r), is thus constant in the central part and then decreases as the same power law. In the smooth model, the gas fills the core completely, and its local density exactly follows the mean density of the clumpy model. For both models, each clump has thermal as well as bulk motions, velocity dispersion of the latter being proportional to r0.5. In the clumpy structured core, the excitation temperature of the CS transitions is found to be generally constant over an entire region. As a consequence, the synthesized profile is of a Gaussian shape superposed with some wiggles, which reflects the existence of clumps under the bulk motion. The trend of flat distribution of excitation temperature becomes more prominent for optically thin transitions of the rarer species C34S. The profiles develop flat-top features with minor wiggles only when the core becomes extremely thick in the optical sense. On the other hand, wider profiles that have self-absorption are synthesized in the smooth core. The self-absorption is formed by a steep gradient in the radial distribution of the excitation temperature. For optically thin C34S transitions, both the clumpy and the smooth cores exhibit profiles close to a Gaussian shape. Comparing line parameters derived in the Monte Carlo code and those by the large-scale velocity gradient calculations, we found that only the clumpy models can give correct estimations of the density and abundance of the cores. Moreover, we have shown that clump parameters, such as clump size and number of clumps in a beam, are reasonably estimated by Tauber's simple method. Since the opaque line reflects properties of a region of τ ~ 1, local unbalance of bulk velocity distribution in the core, for instance, often results in a blue peak stronger than the red peak in the CS line profiles. Thus it should be noted that a combination of this feature of the optically thick line and the single peak of the thin one may not necessarily imply a signature of infall.