Engineering topics
Publications and source records attributed to Sastry, K. V. L. N..
We discuss past and recent progress in our long-term laboratory program concerning the submillimeter-wave rotational spectroscopy of known and likely interstellar molecules, especially those associated with regions of high-mass star formation. Our program on the use of spectroscopy to study rotationally inelastic collisions of interstellar interest is also briefly mentioned.
C2H5CN (Propionitrile or ethyl cyanide) is a well known interstellar species abundantly observed in hot cores during the onset of star formation. The onset of star formation generally results in elevated temperature, which thermally populates may low lying vibrational states such as the 206/cm in-plane bend and the 212/cm first excited torsional state in C2H5CN. Unfortunately, these two states are strongly coupled through a complex series of torsion-vibration-rotation interactions, which dominate the spectrum. In order to understand the details of these interactions and develop models capable of predicting unmeasured transitions for astronomical observations in C2H5CN and similar molecules, several thousand rotational transitions in the lowest excited in-plane bend and first excited torsional state have been recorded, assigned and analyzed. The analysis reveals very strong a- and b-type Coriolis interactions and a number of other smaller interactions and has a number of important implications for other C3V torsion-rotation-vibration systems. The relative importance and the physical origins of the coupling among the rotational, vibrational and torsional motions will be presented along with a full spectroscopic analysis and supporting astronomical observations.
Ethyl alcohol (ethanol) is known to possess a pair of closely spaced excited torsional substates (gauche+, gauche-) at an energy of approximately 57 K above the ground (trans) torsional substate. We report an extended analysis of some gauche - gauche+ Q-branch ((Delta)J = 0) transitions with a three-substate fixed frame axis method (FFAM) Hamiltonian. Our approach accounts for complex trans-gauche interactions for the first time. In addition, we are able to obtain intensities for perturbed rotational transitions, and to determine the trans to gauche+ separation to be 1185399.1 MHz. A complete ground state rotational-torsional partition function accounting for the previously neglected gauche substates is presented. Based on our analysis, a total of 14 U lines obtained towards Orion KL can now be assigned to gauche substates of ethanol. Analysis of these lines yields a rotational temperature of 223 K and a total (trans + gauche) column density of 7.0 x 10(exp 15)/sq cm. The column density is in reasonable agreement with the recent value of 2-3 x 10(exp 15)/sq cm based on observations of trans-ethanol by Ohishi et al., although there is some disparity in the rotational temperatures. Eight additional U lines in the literature are assigned to transitions of gauche ethanol.
We report an investigation of the rotational-torsional spectrum of the gauche rotational isomers of ethyl alcohol in the 51-505 GHz frequency region. Over a thousand transitions between rotational levels in the gauche substates of the ground OH torsional state have been measured and assigned. These transitions involve rotational quantum numbers J and K(sub a) up to 30 and 15, respectively, and are of two types: alpha-type transitions between levels in either the gauche+ or the gauche-substate, and c-type transitions between rotational levels in the different substates. The majority of these transitions have been fit satisfactorily using a two-state Hamiltonian based on the Fixed Framework Axis Method (FFAM). The rotation, distortion, and interaction constants have been determined along with the energy difference between the two gauche substates. The derived constants can be used to predict many more transitions accurately for astronomical purposes. The J and K(sub a) region where the two-state analysis can be used has been determined. The basis for a three-state analysis including the trans substate is presented and the applicability of the FFAM approach is discussed.
Ethyl alcohol (ethanol) is known to possess a pair of closely-spaced excited torsional substates (gauche +, gauche -) at an energy of approximately 57 K above the ground (trans) torsional substrate. We report an extended analysis of some gauch- - gauch+ Q branch (delta J=0) transitions witha three-substrate fixed frame axis method (FFAM) Hamilton.
We report an investigation of the rotational-torsional spectrum of the gauche rotational isomers of ethyl alcohol in the 51е05 GHz frequency region. Over a thousand transitions between rotational levels in the gauche substates of the ground OH torsional state have been measured and assigned. These transitions involve rotational quantum numbers J and Ka up to 30 and 15, respectively, and are of two types: a-type transitions between levels in either the gauche+ or the gaucheРsubstate, and c-type transitions between rotational levels in the different substates. The majority of these transitions have been fit satisfactorily using a two-state Hamiltonian based on the fixed framework axis method (FFAM). The rotation, distortion, and interaction constants have been determined along with the energy difference between the two gauche substates. The derived constants can be used to predict many more transitions accurately for astronomical purposes. The J and Ka region where the two-state analysis can be used has been determined. The basis for a three-state analysis including the trans substate is presented and the applicability of the FFAM approach is discussed.!
The laboratory millimeter-wave and submillimeter-wave rotational spectrum of propionitrile (ethyl cyanide, C2H5CN) in its ground vibrational state has been extended through J = 70 and K(sub a) = 36. Transitions measured in this study are in the frequency range 250-610 GHz. A fit of 952 transitions including 732 new measurements to a Watson A-reduced Hamiltonian has yielded a complete set of quartic and sextic distortion constants, in addition to six octic distortion constants. Internal rotation and hyperfine splittings have not been resolved, so they are not included in the analysis. Predicted transition frequencies for a large number of additional transitions of interest to radioastronomers are provided.
The rotational-torsional spectrum of (C-13)H3OH is presented in both the symmetric and degenerate substates of the first two excited torsional states. Of the new transitions reported, 122 lines are from the v(t) = 1 torsional state and 110 lines are from the v(t) = 2 torsional state, and all are confined to the rotational quantum number J = 8 or less. The data are combined with previously reported millimeter and submillimeter data for the v(t) = 0 torsional state and 44 previously measured excited torsional state lines to form a global data set of 596 transitions, which is analyzed and fitted using an extended internal axis method. The fit results in an overall rms deviation of 1.98 MHz. The spectral constants generated by the fit are used to predict an additional 123 lines of (C-13)H3OH in the v(t) = 1,2 excited torsional states with frequencies up to 612 GHz and rotational quantum number J = 11 or less.
The identification of interstellar molecular species via the detection of one spectral line has recently become subject to close scrutiny. The radical HNO falls into the class of interstellar molecules identified in this manner. To corroborate this identification, observation of additional spectral lines is necessary. In this paper, laboratory millimeter and submillimeter wave spectra of both HNO and DNO are reported in the frequency region 150-500 GHz. Based on these spectral line measurements, models for HNO and DNO have been constructed to yield accurate frequencies for all rotational transitions of these species below 500 GHz involving J values smaller than 10. The spectral lines can be utilized by radio astronomers to confirm the identification of interstellar HNO and to search for interstellar DNO.
The rotational absorption frequencies of 68 new lines from the HCO radical in its ground electronic state have been measured in the millimeter and submillimeter spectral region. The large zero-field data set acquired has allowed the complex spectrum of this light asymmetric rotor with unpaired electronic spin and magnetic hyperfine interactions to be completely analyzed to within experimental accuracy for the first time. The wide range of states observed provides a highly accurate map of the rotational frequencies of the formyl radical, which should enable the abundance and excitation of interstellar HCO to be examined in detail.
The laboratory millimeter and submillimeter spectrum of the interstellar radical CCH has been observed and measured in the 174-350 GHz region. The fitted spectral constants are in excellent agreement with those determined from radioastronomical measurement.
The strong electric dipole-allowed transitions of the molecular ion CO(+) in the region 235-470 GHz have been measured in the laboratory. The laboratory spectra at 235 GHz appear to confirm the claim by Erickson et al. (1981) to have observed CO(+) in OMC-1.
The J = 0-1 transitions of six different isotopic forms of the HCO(+) molecular ion, which were investigated by Woods et al. (1975), are considered. The extension of this work into the shorter millimeter and submillimeter region is reported here, as is the measurement of these spectra through J = 4-5 for HCO(+) and J = 5-6 for DCO(+). It is noted that these measurements can be used to determine accurate rotational constants and rest frequencies for these astrophysically important species. Tables listing the observed rotational constants and spectral constants of HCO(+) and DCO(+) are included.
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