Cold Dark Clouds Research Articles

A Search for MgNC and AlNC in TMC‐1: The Status of Metals in Dark Cloud Cores

Heavy metals in the gas phase are important in controlling the ionization of a cold dark cloud and hence the chemistry and finally the cloud evolution. Two of us (S. P. and R. C. D.) earlier suggested a fast radiative association mechanism to form MgNC and AlNC in TMC-1. We have conducted a sensitive search with the Green Bank Telescope (GBT) for both species in TMC-1. The upper limit for the fractional abundance of MgNC is 1.2 × 10-11. We have run detailed models of the chemistry, which include high and low metal content, three values of C/O, and three values of density. The models include the time dependence up to 1 × 108 yr. Most of the models predict that we should have seen MgNC. We compare the conditions in TMC-1 with those for IRC +10216, in which MgNC and AlNC are both detected. We conclude that in IRC +10216 the chemistry favors a high abundance of both atomic Mg+ and cyanopolyynes, the two reactants that form MgNC, and that these reactants are less favored in TMC-1.

A Survey of Large Molecules of Biological Interest toward Selected High‐Mass Star‐forming Regions

We have surveyed three high mass Galactic star forming regions for interstellar methanol (CH3OH), formic acid (HCOOH), acetic acid (CH3COOH), methyl formate (HCOOCH3), methyl cyanide (CH3CN), and ethyl cyanide (CH3CH2CN) with the BIMA Array. From our observations, we have detected two new sources of interstellar HCOOH toward the hot core regions G19.61-0.23 and W75N. We have also made the first detections of CH3CH2CN and HCOOCH3 toward G19.61-0.23. The relative HCOOH/HCOOCH3 abundance ratio toward G19.61-0.23 is 0.18 which is comparable to the abundance ratios found by Liu and colleagues toward Sgr B2(N-LMH), Orion and W51(approximately 0.10). We have made the first detection of HCOOCH3 toward W75N. The relative HCOOH/HCOOCH3 abundance ratio toward W75N is 0.26 which is more than twice as large as the abundance ratios found by Liu and colleagues. Furthermore, the hot core regions around W75N show a chemical differentiation between the O and N cores similar to what is seen toward the Orion Hot Core and Compact Ridge and W3(OH) and W3(H2O). It is also apparent from our observations that the high mass star forming region G45.47+0.05 does not contain any compact hot molecular core and as a consequence its chemistry may be similar to cold dark clouds. Finally, the formation of CH3COOH appears to favor HMCs with well mixed N and O, despite the fact that CH3COOH does not contain a N atom. If proved to be true, this is an important constraint on CH3COOH formation and possibly other structurally similar biomolecules.

Accurate rest frequencies of methanol maser and dark cloud lines

We report accurate laboratory measurements of selected methanol transition frequencies between 0.834 and 230 GHz in order to facilitate astronomical velocity analyses. New data have been obtained between 10 and 27 GHz and between 60 and 119 GHz. Emphasis has been put on known or potential interstellar maser lines as well as on transitions suitable for the investigation of cold dark clouds. Because of the narrow line widths (<0.5 kms-1) of maser lines and lines detected in dark molecular clouds, accurate frequencies are needed for comparison of the velocities of different methanol lines with each other as well as with lines from other species. In particular, frequencies for a comprehensive set of transitions are given which, because of their low level energies (< 20 cm-1 or 30 K) are potentially detectable in cold clouds. Global Hamiltonian fits generally do not yet yield the required accuracy. Additionally, we report transition frequencies for other lines that may be used to test and to improve existing Hamiltonian models.

Interstellar and Circumstellar Reaction Kinetics of Na+, Mg+, and Al+with Cyanopolyynes and Polyynes

We report calculated rate coefficients for the radiative association reactions of M+ (Na+, Mg+, or Al+) with cyanopolyynes HC2n+1N (n = 0-4) and polyynes HC2nH (n = 1-5), at temperatures relevant to conditions within dense interstellar clouds and the outer envelopes of mass-losing stars. These reaction rate coefficients were determined via variational transition state theory kinetic modeling calculations employing structural, energetic, and spectroscopic parameters obtained from density functional theory calculations. We have performed simple kinetic modeling of these reactions within a cold dark cloud (TMC-1) and within the outer envelope of a C-rich, post-asymptotic giant branch mass-losing star (IRC +10216), with molecular compositions and other parameters of these environments taken from current chemical models. This modeling indicates that the highly efficient radiative association reactions of Mg+ and Al+ with HC5N and HC7N, and of Na+ with HC7N, give a drastic reduction in the lifetime of the atomic metal ions in these environments compared with a model in which radiative recombination of M+ with e- is the sole metal-ion loss process. These results also provide further support to the hypothesis that M+/cyanopolyyne reactions are the route to metal cyanide radicals such as MgCN and MgNC in cold astrophysical environments.

Interstellar methanol masers

The asymmetric rotor molecule methanol (CH3OH) has hundreds of transitions at centimeter-, millimeter-, and submillimeter wavelengths. Many of these are excited in the hot (T ≳ 150 K), dense (n ≳ 106 cm−3) molecular cloud cores surrounding newly formed massive stars or protostars. The high temperatures in these cores cause evaporation of icy grain mantles, releasing copious amounts of complex molecules, such as methanol, in the gas phase, which in hot cores has abundances (up to 10−6 relative to H2) that are two or more orders of magnitude higher than in cold dark clouds.

Deuterated Molecules in Translucent and Dark Clouds

We present observations of 10 deuterated molecular species in the dark clouds TMC-1, L183, and the translucent object CB 17, as well as a subset of species in and other objects. With sensitive TMCNH 3 observations of the J 1¨0 and 2¨1 transitions of DCN, and DNC, we have been able to derive N 2 D‘, molecular constants that include the complex nuclear quadrupole hyper—ne splitting in these species, which is essential to determine accurate abundances. The spectroscopic results have required, in turn, new radiative transport techniques to handle the hyper—ne eUects. Our abundance determinations also utilize sensitive observations of secondary isotopomers involving 13C, 18O, and 15N. Compared with earlier molecular D/H ratios in the literature, these innovations have resulted in radically diUerent values in some cases in TMC-1 and in TMC-1; DCN/HCN in CB 17), (N 2 D‘/N 2 H‘ TMCNH 3 ;N H 2 D/NH 3 and important modi—cations in others in TMC-1). The new techniques usually produce (C 3 HD/C 3 H 2 deuteration ratios lower than those obtained earlier by simpler methods. Thus, in addition to the special cases noted above, our results are generally lower than previous ones by factors of typically 2. We also —nd that deuteration occurs only in regions of high density, while nondeuterated species generally reside at lower densities. A recently proposed model of translucent clouds as low-density objects containing embedded small, high-density fragments explains the observations. To study the chemistry of deuterated species, we have used the New Standard Model, modi—ed to include all monodeuterated species, and now containing 9930 reactions and 610 species. Our models explore the dependence of the molecular D/H ratios upon temperature, density, ionization rate, extinction, epoch, and elemental abundances. Within the uncertainties, we —nd agreement between observed and modeled ratios for nearly all species in nearly all sources. Our results generally agree with those of Roberts & Millar in a recent, similar study. We —nd signi—cantly higher ratios in L183 than in TMC, and intermediate values in CB 17. With our lower values in general, however, we believe that L183 is ii normal ˇˇ for a cold dark cloud, CB 17 is typical of a slightly warmer translucent object, and the TMC region is perhaps underdeuterated in general, certainly strongly so in the case of and These N 2 H‘ NH 3 . ii anomalous ˇˇ cases have no plausible single explanation in terms of gas-phase chemistry at this time. Grain processes are implicated. . .. . .. . ..

Constraints on the Formation of Comets from D/H Ratios Measured in H 2O and HCN

This report is the follow-up of the paper of A. Drouart et al. (1999, Icarus 140, 129) in which it was demonstrated that appropriate models of the solar nebula permit us to interpret the deuterium enrichment in water with respect to the protosolar D/H ratio measured in LL3 meteorites and comets. In the present report, we show that the models selected by Drouart et al. are also able to explain D/H in HCN measured in Comet C/1995 O1 (Hale–Bopp). We find that the D/H ratio in HCN entering the nebula is ∼4×10 −3, which is significantly less than values measured in cold dark clouds, but consistent with values found in hot molecular cores. Both H 2O and HCN ices infalling from the presolar cloud onto the nebula discoid evaporated in the turbulent part of the nebula, isotopically exchanged with hydrogen, and mixed with water vapor coming from the inner part of the nebula. Subsequently, H 2O and HCN ices with D/H ratios measured in Comet Hale–Bopp condensed, agglomerated and were incorporated in cometesimals. In the light of these results, we discuss the story of molecules detected in comets coming from Oort cloud. Most molecules detected in Comet Hale–Bopp originated from ices embedded in the presolar cloud. Ices vaporized prior to entering into the nebula or in the early nebula, and subsequently recondensed, except highly volatile molecules. According to A. Kouchi et al. (1994, Astron. Astrophys. 290, 1009), water ice condensed in crystalline form. We discuss the possibility that the most volatile species were then trapped in the form of clathrate hydrates. The oversolar C/N ratio and the strong depletion of Ne/O with respect to the solar abundance observed in comets are in agreement with the theory of clathrate hydrates of J. I. Lunine and D. J. Stevenson (1985, Astrophys. suppl. Ser. 58, 493). Comets formed in the Kuiper belt may contain amorphous water ice and have kept the isotopic signature of the presolar cloud. New published models of interiors of Uranus and Neptune permit us to calculate that the D/H ratios in proto-uranian and proto-neptunian water ices are in agreement with those measured in comets. This confirms the current assumption that cometesimals and planetesimals that formed the cores of Uranus and Neptune had similar compositions.

Observations of NH \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $_{2}$ \end{document} D toward Dark Molecular Clouds

The 1-1 transition of NH2D at 110.1536 GHz was surveyed toward 16 cores of high ammonia abundance in 14 cold dark clouds and was detected toward eight cloud cores, L1448, B1, L1489N, L1551N, L1641N, L134N(S), ρ Oph E, and L63, where L134N and L63 are not associated with infrared sources. The column densities of NH2D were compared with those of the main species NH3, previously determined for the corresponding sources, and the relative abundance, [NH2D]/[NH3], was found to be large, 0.025-0.18, which is among the highest deuterium fractionation so far observed. The relative abundance is remarkably larger than a predicted value by the latest gas-phase chemical model for dark clouds by Howe & Millar. The spectral line of NH2D was not detected in other dark cloud cores. These results suggest that a part of NH3 in dark clouds could originate from dust related reactions associated with energetic events.

The Physics and Chemistry of Small Translucent Molecular Clouds. XI. Methanol

We have made a survey of CH3OH in 27 of our standard sample of 11 cirrus cores and 27 Clemens-Barvainis translucent cores whose structures and chemistry have been studied earlier in this series. CH3OH is detected in 17 objects, favoring those with larger extinctions. The mean fractional abundance is 1(-8), but if the four highest abundance objects are omitted, the mean abundance is 3(-9), the same as in two cold dark clouds. Collision rates remain poorly known for CH3OH, but uncertainties in propensity rules are shown not to affect abundances more than 10%. The geometric component of the rates is uncertain by a factor of 2; hence, also, the abundances. The gas-phase chemistry is particularly simple, formation occurring only via the radiative association reaction CH -->+3+H -->2O?CH -->3OH -->+2+h? followed by electron recombination. We have verified the predictions of this simple model by using the full Standard Model of over 3000 reactions, with conditions suitable for translucent clouds. These gas-phase models predict abundances 4 orders of magnitude less than the observed abundances. We have examined grain surface chemistry in which accreted CO hydrogenates to CH3OH on the surface under the action of UV or cosmic rays and then desorbs in various ways, photodesorption dominating. Despite the uncertainties of the grain processes, they can easily explain the observed abundances and in fact imply much lower desorption efficiencies than are usually adopted. Methanol is of intermediate complexity, as are several other species we will study in the next papers, with the goal of testing the boundary between gas-phase and grain chemistry, the latter believed to be important for the most complex species.

The Polarizing Power of the Interstellar Medium in Taurus

We present a study of the polarizing power of the dust in cold dense regions (dark clouds) compared to that of dust in the general interstellar medium (ISM). Our study uses new polarimetric, optical, and spectral classification data for 36 stars to carefully study the relation between polarization percentage (p) and extinction (A_V) in the Taurus dark cloud complex. We find two trends in our p-A_V study: (1) stars background to the warm ISM show an increase in p with A_V; and (2) the percentage of polarization of stars background to cold dark clouds does not increase with extinction. We detect a break in the p-A_V relation at an extinction 1.3 +/- 0.2 mag, which we expect corresponds to a set of conditions where the polarizing power of the dust associated with the Taurus dark clouds drops precipitously. This breakpoint places important restrictions on the use of polarimetry in studying interstellar magnetic fields.

Laboratory Microwave Spectroscopy of HDCS and Its Astronomical Detection toward TMC-1

The rotational spectrum of the deuterated species of thioformaldehyde, HDCS, has been measured in the laboratory by microwave spectroscopy. Fifty-two a-type R-branch transitions are observed, and the rotational constants and centrifugal distortion constants are determined accurately. On the basis of the laboratory results, two unidentified lines detected during the line survey toward a cold dark cloud TMC-1 are assigned to HDCS. The [HDCS]/[H2CS] ratio is determined to be 0.020 ± 0.005, indicating relatively high deuterium fractionation in H2CS. The ratio is discussed in terms of formation processes of H2CS in dark clouds.

Does Near-Infrared Polarimetry Reveal the Magnetic Field in Cold Dark Clouds?

view Abstract Citations (161) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Does Near-Infrared Polarimetry Reveal the Magnetic Field in Cold Dark Clouds? Goodman, Alyssa A. ; Jones, Terry J. ; Lada, Elizabeth A. ; Myers, Philip C. Abstract We present near-infrared (JHK) observations of the polarization of background starlight seen through the filamentary dark cloud L1755. The mean position angle and dispersion of the polarization vectors measured in the near-infrared, for stars along lines of sight passing through the densest portions (1 < Av < 10 mag) of L1755, are virtually identical to those in an optical polarization map of stars around the periphery (Av ∼ 1 mag) of L1755. Furthermore, the percentage of polarization is not seen to increase, at all, with extinction in the near-infrared observations. We surmise that much of the dust in the dark cloud is extinguishing background starlight significantly, but not polarizing it efficiently, and thus that the polarization map of background starlight cannot reliably trace the magnetic field associated with the dense interior of the dark cloud. Our results in L1755 are remarkably similar to what we found in the dark cloud B216-217 (Goodman et al. 1992), which also shows no change in the polarization map associated with the cloud, and no rise in percentage polarization with extinction. Using our multiwavelength polarimetric observations of L1755, we have estimated the wavelength of maximum polarization, λmax, for most of the 53 stars in our sample. We find an unusually broad distribution of λmax, with a mean at 0.88±0.34 μm. The large range of λmax leads us to the hypothesis that there is a wide range of grain sizes and/or shapes along the lines of sight through L1755. We conclude that only a small subset of grains is responsible for producing the polarization of background starlight, and that these grains may be critically underrepresented in the dense interiors of cold dark clouds. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176003 Bibcode: 1995ApJ...448..748G Keywords: INFRARED: ISM: CONTINUUM; ISM: CLOUDS; ISM: DUST; EXTINCTION; ISM: INDIVIDUAL ALPHANUMERIC: L1755; ISM: MAGNETIC FIELDS; POLARIZATION full text sources ADS | data products SIMBAD (60)

Molecular Abundances and Low-Mass Star Formation. II. Organic and Deuterated Species toward IRAS 16293-2422

view Abstract Citations (305) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Abundances and Low-Mass Star Formation. II. Organic and Deuterated Species toward IRAS 16293-2422 van Dishoeck, Ewine F. ; Blake, Geoffrey A. ; Jansen, David J. ; Groesbeck, T. D. Abstract Millimeter and submillimeter line surveys of the protobinary source IRAS 16293-2422 are presented in the 230 and 345 GHz windows. In total, 265 lines belonging to 44 molecules and their isotopomers (24 chemically different species) have been detected. Here the data for organic and deuterated molecules are considered; the results for Si- and S-bearing species have been discussed in an earlier paper (Blake et al. 1994). The observations have been analyzed through a combination of rotation diagrams and full statistical equilibrium/ radiative transfer calculations. At least three physically and chemically different components can be distinguished within the 20" (3000 AU) beam. The first component is the warm (Tkin ≳ 80 K) and dense [n(H2) ≍ (0.5-1) × 107 cm-3] gas sampled by Si- and S-containing molecules such as SiO and SO2. This gas is found to be rich in organic molecules such as CH3OH, CH3CN, and H2CO, as well. It is only 3"-10" in size (500-1500 AU) and most likely represents the interaction of the bipolar outflow(s) with the circumbinary envelope. The second component is the circumbinary envelope itself, which has Tkin 40 K and n(H2) 106 - 107 cm-3 and is 10"-15" in size (2000 AU). It contains common molecules like CS, HCO+, and H2CO. The third component is the colder, lower density outer part of the envelope, which gradually fades into the ambient surrounding cloud core [Tkin ≍ 10-20 K; n(H2) (3 × 104)-(2 × 105) cm-3]. Radicals such as CN, C2H, and C3H2 appear to reside principally in this region. The ambient cloud material is also probed through self-absorbed features in the line profiles of molecules such as HCN, HCO+, and H2CO. Beam-averaged abundances over a 20" scale are presented and are compared with those observed in cold dark clouds such as L134N and TMC-1 and with high-mass star-forming cores such as Orion-KL. Remarkably high deuterium fractionation ratios are found, which are more characteristic of hot core regions than of cold, quiescent clouds. As a whole, the chemical and physical regimes that can be distinguished in the low-mass young stellar object IRAS 16293-2422 are qualitatively similar to those found in high-mass star-forming regions, confirming the earlier conclusion that the chemical composition depends more on the age of the object than its mass. Publication: The Astrophysical Journal Pub Date: July 1995 DOI: 10.1086/175915 Bibcode: 1995ApJ...447..760V Keywords: ISM: MOLECULES; STARS: CIRCUMSTELLAR MATTER; STARS: INDIVIDUAL ALPHANUMERIC: IRAS 16293-2422; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (10) Related Materials (1) Part 1: 1994ApJ...428..680B

Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption

We present time-dependent models of the chemical evolution of molecular clouds which include depletion of atoms and molecules onto grain surfaces and desorption, as well as gas-phase interactions. We have included three mechanisms to remove species from the grain mantles: thermal evaporation, cosmic-ray-induced heating, and photodesorption. A wide range of parameter space has been explored to examine the abundance of species present both on the grain mantles and in the gas phase as a function of both position in the cloud (visual extinction) and of evolutionary state (time). The dominant mechanism that removes molecules from the grain mantles is cosmic-ray desorption. At times greater than the depletion timescale, the abundances of some simple species agree with abundances observed in the cold dark cloud TMC-1. Even though cosmic-ray desorption preserves the gas-phase chemistry at late times, molecules do show significant depletions from the gas phase. Examination of the dependence of depletion as a function of density shows that when the density increases from 10(exp 3)/cc to 10(exp 5)/cc several species including HCO(+), HCN, and CN show gas-phase abundance reductions of over an order of magnitude. The CO: H2O ratio in the grain mantles for our standard model is on the order of 10:1, in reasonable agreement with observations of nonpolar CO ice features in rho Ophiuchus and Serpens. We have also examined the interdependence of CO depletion with the space density of molecular hydrogen and binding energy to the grain surface. We find that the observed depletion of CO in Taurus in inconsistent with CO bonding in an H2O rich mantle, in agreement with observations. We suggest that if interstellar grains consist of an outer layer of CO ice, then the binding energies for many species to the grain mantle may be lower than commonly used, and a significant portion of molecular material may be maintained in the gas phase.

Nitrogen sulfide in quiescent dark clouds.

We report the first detection of interstellar nitrogen sulfide (NS) in cold dark clouds. Several components of the 2 pi 1/2, J = 3/2 --> 1/2 and J = 5/2 --> 3/2 transitions were observed in TMC-1 and L134N. The inferred column density for TMC-1 is NNS approximately 8 x 10(12)cm-2 toward the NH3 peak in that cloud, and in L134N is NNS approximately 3 x 10(12)cm-2 toward the position of peak NH3 emission. These values correspond to fractional abundances relative to molecular hydrogen of fNS approximately 8 x 10(-10) for TMC-1, and fNS approximately 6 x 10(-10) for L134N. The NS emission is extended along the TMC-1 ridge and is also extended in L134N. The measured abundances are significantly higher than those predicted by some recent gas phase ion-molecule models.

Mapping observations of sulfur-containing carbon-chain molecules in Taurus Molecular Cloud 1 (TMC-1)

High-resolution mapping observations were carried out toward Taurus Molecular Cloud 1 (TMC-1) with sulfur-containing carbon-chain molecules, CCS and C 3 S, and other molecules, CS, C 34 S, HCS + , HC 3 N, HC 5 N, C 4 H, and NH 3 , to investigate detailed molecular distribution and physical structure of the cold dark cloud.

A survey of N2H(+) in dense clouds - Implications for interstellar nitrogen and ion-molecule chemistry

Spectra of the N 2 H + J=1→0, J=3→2 and 15 NNH + and N 15 NH + J=1→0 rotational transitions have been obtained toward a sample of star-forming and cold dark clouds in the Galaxy. Toward the star-forming regions, line profiles are relatively narrow (typically 1-5 km/s) and show no evidence of line wings, in contrast to the spectra of HCO + . The apparent absence of N 2 H + in hot, shocked gas suggests that this ion may be a selective tracer of extended, quiescent material

C60: Buckminsterfullerene, The Celestial Sphere that Fell to Earth

AbstractIn 1975–1978 the long‐chained polyynylcyanides, HC5N, HC7N, and HC9N were surprisingly discovered in the cold dark clouds of interstellar space by radioastronomy. The subsequent quest for their source indicated that they were being blown out of red giant, carbon stars. In 1985 carbon‐cluster experiments aimed at simulating the chemistry in such stars confirmed these objects as likely sources. During these cluster studies a serendipitous discovery was made; a stable pure‐carbon species, C60, formed spontaneously in a chaotic plasma produced by a laser focused on a graphite target. A closed spheroidal cage structure was proposed for this molecule, which was to become the third well‐characterized allotrope of carbon and was named buckminsterfullerene. It has taken five years to produce sufficient material to prove the correctness of this conjecture. There may be a timely object lesson in the fact that exciting new and strategically important fields of chemistry and materials science have been discovered overnight due to fundamental research, much of which was unable to attract financial support, and all of which was stimulated by a fascination with the role of carbon in space and stars. In this account, interesting aspects of this discovery, its origins, and its sequel are presented. The story has many facets, some of which relate to the way scientific discoveries are made.

Rotational spectrum of the CCS radical studied by laboratory microwave spectroscopy and radio-astronomical observations

The rotational spectral lines of the CCS radical and its isotopic species, CC(S-34), (C-13)CS, and C(C-13)S, have been observed in the laboratory, and the J(N) = 4(3)-3(2), J(N) = 2(1)-1(0), and J(N) = 3(4)-2(3) transitions for CCS and that of J(N) = 4(3)-3(2) for CC(S-34) have been observed toward a cold dark cloud, L1498. The molecular constants of CCS, CC(S-34), (C-13)CS, and C(C-13)S have been determined from the observed transition frequencies, and the rest frequencies of CCS and CC(S-34) below 300 GHz are listed with their line strengths. The frequencies of the low-N transitions of (C-13)CS and C(C-13)S are calculated for future astronomical observations. 19 refs.

Detection of nitric oxide in the dark cloud L134N.

We report the first detection of interstellar nitric oxide (NO) in a cold dark cloud, L134N. Nitric oxide was observed by means of its two 2 pi 1/2, J = 3/2 --> 1/2, rotational transitions at 150.2 and 150.5 GHz, which occur because of lambda-doubling. The inferred column density for L134N is N(NO) approximately 5 x 10(14) cm-2 toward the SO peak in that cloud. This value corresponds to a fractional abundance relative to molecular hydrogen of f(NO) approximately 6 x 10(-8) and is in good agreement with predictions of quiescent cloud ion-molecule chemistry. NO was not detected toward the dark cloud TMC-1 at an upper limit of f(NO) < or = 3 x 10(-8).