SUBWOOFERS
Power Handling 2000 watts RMS / 2500 watts Peak Industrial design marries traditional HCCA styling cues with cutting edge technology Massive proprietary die-cast basket supports integrated Dual Gap motor assembly Ultra-rigid heat-hardened aluminum cone and tough NBR surround 3" two layer copper voice coil on aluminum former Proprietary AngleLock wiring terminals Die-cast mounting clamps integrated into tooled wrap-gasket Dual 2 or dual 4 ohm models in 10", 12", and 15" Winner of CES Innovations Award
SUBWOOFER POWER Fs.2 Fs.4 Qts.2 Qts.4 Vas.2 Vas.4 SENSITIVITY LINEAR EXCURSION DIMENSIONS ______________________________________________________________________________________________________
ENCLOSURE POWER SERIES SIZE IMPEDANCE FREQ. RESPONSE EFF DIMENSIONS ______________________________________________________________________________________________________
SPEAKER POWER NOMINAL IMPEDANCE FEATURES FREQ. RESPONSE SENSITIVITY DEPTH ______________________________________________________________________________________________________
Power Handling 200 watts RMS / 400 watts Peak Heavy Gauge Steel Basket Non-resonant Poly cone and synthetic rubber surround Poly-cotton Blend Spider Extended Vented Pole Piece Gold-plated Strain Relief Terminals Dual 2 or dual 4 ohm models in 10" and 12"

2.3/8 / 59mm

2 3/16 / 56mm

3 1/8 / 80mm

2 1/4 / 57mm

2 7/8 / 73mm

9.25 / 7.5

14 / 9.25

11.25 / 8

_________________

C-SERIES

COMPONENTS

features
Power Handling 50 watts RMS / 100 watts Peak for C5.2 and 75 watts RMS / 125 watts Peak for C6.2 Ideal for Upgrading Any Sound System Steel Baskets Fit Standard OEM Applications Euro-compatible Design 19mm Ceramic Dome Tweeters Swivel, Flush and Surface Mount Harness Offboard Passive 12 dB/Octave Crossovers

125 watts

8.75 / 5

11 / 7

3 / 76mm

9 / 6.5

11 / 6

2 3/4 / 71mm

32 x 21 x 14.5

30 x 19 x 13.5

60Hz 20kHz

55Hz 20kHz

80Hz 20kHz

85Hz 20kHz

H2 10.2

2.99 cu ft

1.24 cu ft

0.45 cu ft

1.79 cu ft

0.62 cu ft

4.42 cu ft
Low impedance to provide 33% more power.
19mm ceramic dome tweeters.

Parallel to 1 ohm

Power Handling 500 watts RMS / 1000 watts Peak Machined Custom Die-Cast Basket Open Loop Motor Design Metallized Poly Cone and Medium Roll NBR Surround Tight Small Sealed Box Performance Custom Tooled Reversible Wrap Gasket and Protective Magnet Boot Heavy Gauge Wire Terminals 2.5 Inch Voice Coil on Aluminum Former
Dual 10 and watt vented pre-loaded enclosures Custom-tuned vented enclosures providing punishing bass output levels Features hot new HP-series Open Loop subwoofers Value-add badging makes drop-in sales easy

COAXIALS

Ideal for upgrading any Sound System 3 ohm voive coils for maximum output from your radio Steel Baskets Fit Standard OEM Applications Euro-compatible Design 19mm Ceramic Dome Tweeters Swivel, Flush and Surface Mount Harness Offboard Passive 12 dB/Octave Crossovers

27.75Hz

9mm ceramic dome tweeters.

ENCLOSURES

50 watts

75 watts

1.32 cu ft

2500 watts

H2 12.2

H2 15.2

C2 102/104

400 watts

C2 122/124
1 titanium dome tweeter. Surface, angled, and flush mounting hardware Included.

1.78 cu ft

0.56 cu ft

1.63 cu ft

45Hz 20kHz

87 / 85dB

85 / 83dB

87 / 86dB

75Hz 20kHz

91 / 89dB

90Hz 20kHz
Power Handling 125 watts RMS / 175 watts Peak Proprietary Orion Tooled Die-Cast Baskets Aluminum Vapor Deposit Injection-molded Poly Cone 6mm Linear One-way Excursion for Up-front Bass Tough Santoprene Surround for Enhanced Low Frequency Response One Inch Vapor Deposit Titanium Dome Tweeter Biampable 18 dB/Octave Crossover Tweeter Level and Polarity Switches
SPEAKER SPECIFICATIONS SPEAKER SPECIFICATIONS

P-SERIES

29.46Hz

2 x 12

40 watts

______________

2000 watts continuous / 2500 watts peak
500 watts continuous / 1000 watts peak
200 watts continuous / 400 watts peak

4 ohms

3 ohms

BP-HP10D4

1000 watts peak x 2

2000 watts

125 / 175 watts

75 / 125 watts

50 / 100 watts

40 / 80 watts

BP-HP12D4

HP-10D2 / 4

HP-12D2 / 4

HP 10D2/10D4

1000 watts

HP 12D2/12D4

C/ 104

C/ 124

Orion HP

2 x 10

22.8 x 10.2 x 2.4 (580mm x 260mm x 61mm)
12.6 x 10.2 x 2.4 (320mm x 260mm x 61mm)
7.9 x 10.2 x 2.4 (200mm x 260mm x 61mm)
9.8 x 10.2 x 2.4 (250mm x 260mm x 61mm)
7.0 x 10.2 x 2.4 (180mm x 260mm x 61mm)
AMPLIFIER POWER OUTPUT SIGNAL PROCESSING FUSE SIZE DIMENSIONS __________________________________________________________________________________________________________________
11 x 10.2 x 2.4 (280mm x 260mm x 61mm)
6.3 x 10.2 x 2.4 (160mm x 260mm x 61mm)

ATTITUDE

THE WORLDS LEADING HIGH PERFORMANCE CAR AUDIO BRAND GETS SOME AWESOME NEW UPGRADES IN 2006 Hardcore Attitude
Since the beginning, Orion has been all about High Performance Car Audio and Hardcore Attitude. Attitude thats hammered into the DNA of every piece of industrial-strength Orion Car Audio equipment, and the players who use and abuse it, the bass-heads and boulevard bullies who will testify that the baddest car and the loudest system ride on the same chassistheirs! SPL competitors, world champions, hot-rodders and urban cruisers alike are motivated to roll with the bulletproof performance and legendary muscle that is Orion Car Audio.

HARD-CORE

HIGH CURRENT COMPETITION CLASS D AMPLIFIERS
HIGH PERFORMANCE PURE MOSFET AMPLIFIERS features
Variable low-pass 50Hz to 500kHz, variable high-pass with INTELLi Q 50Hz to 500kHz, 10dB of boost with INTELLi Q, remote gain capable, selectable AUX out
Variable low-pass 30Hz to 250Hz, variable high-pass with INTELLi Q 20Hz to 150Hz, 10dB of boost with INTELLi Q, remote gain capable, selectable AUX out
Proprietary Orion Industrial Design with illuminated badging Directeds patent pending ESP (except model HCCA-D600) Massive loosely-regulated MOSFET power supply IntelliQ Bass Optimization Circuit and RemoteGain Control Heavy Gauge Direct-wire High Current Power and Speaker Terminals 18dB/octave Low-pass Filter
Proprietary Orion Industrial Design with illuminated badging Directeds patent pending ESP (models HP-2800, HP-4800) Massive loosely-regulated MOSFET power supply All new pure MOSFET output stage design Intelli-Bass Equalization Circuit and Remote Gain Option (remote bass optional on models HP-2800, HP-4800) Heavy Gauge Direct-wire High Current Power and Speaker Terminals 12dB/octave High- and Low-pass Filter

MPLIFIER SPECIFICATION

HCCA HPAMPLIFIERS AMPLIFIERS
DIRECTED AUDIO ESSENTIALS ARE ENGINEERED TO OPTIMIZE THE PERFORMANCE OF YOUR ORION AUDIO COMPONENTS, AND RECOMMENDED FOR USE WITH ALL OTHER BRANDS OF FINE MOBILE AUDIO PRODUCTS.
Get the winning performance you expect by matching it with the nest power

(2) 30 ATC

(1) 40 ATC

(2) 20 ATC

(2) 40 ATC

(3) 40 ATC

(2) 15 ATC

(1) 20 ATC

delivery components, cabling and noise-free signal cables available: Directed Audio Essentials! These super-premium audio accessories deliver pure, free-owing sound by utilizing only the highest quality materials and precision machined black chrome-plated components for maximum signal transfer. Oxygen-free copper cabling ensures that nothing is lost or added as the music ows unimpeded from source to destination! Your ampliers will deliver every watt of audio power available when they rely on unbeatable Directed Audio Essentials Power Capacitors and professional grade battery adapters, heavy-duty terminals, fuses and fuse holders. Our award-winning audio adapters offer seamless integration of aftermarket audio systems with original equipment radios. Unwanted vehicle resonance
DIRECTEDS PATENT PENDING ESP
Anti-theft protection and valet mode renders your amp useless to thieves or parking attendants Built-in self-diagnostics allows installer to recall shutdown historyavoids time-consuming service visits Digitally programmed input voltage for fast, accurate system setup Input sensitivity lock-out modelock the tweakers out! Digital control over cooling fan operation, turn-on delay

Variable low-pass 30Hz to 250Hz, variable high-pass with Infrasonic 20Hz to 150Hz, 18dB of boost with INTELLi Bass, remote gain capable
Variable low-pass 50Hz to 500kHz, variable high-pass from 50Hz to 500kHz, 16dB of boost with INTELLi Bass

AMPLIFIER SPECIFICATIONS

Variable low-pass 50Hz to 500kHz, variable high-pass from 50Hz to 500kHz, 10dB of boost with INTELLi Q
and noise is easily tamed with Sound Off damping material. Directed Audio Essentials gives your system the edge
Variable high-pass / low-pass crossover from 50Hz to 500kHz, 16dB of boost with INTELLi Bass

HCCA-D5000

HP-2300
it needs to win in the competition lanes and on the highways!

Orion Technology

Every Orion amp, sub and speaker is designed from the ground up by audio engineers and product specialists dedicated to the heritage, attitude and raw hardcore power of Orion. Never anything off the shelfonly off-the-hook outrageous performance from carefully designed and engineered components, manufactured from pure metals and mil-spec components and to exacting specications. The 2006 Orion Car Audio lineup proudly continues the Orion Industries legacy, standing up once again as the best and the strongest in a market overowing with wanna-bes and chrome-plated posers.

HP-2400

HCCA-D600

HP-2600

100 watts

YOUR AUTHORIZED DEALER

HCCA-D1200

250 watts

YOUR DEALER

HP-4600

1 x 1000 @ 4 ohms / 1 x 1600 @ 2 ohms / 1 x 2500 @ 1 ohm
1 x 425 @ 4 ohms / 1 x 800 @ 2 ohms / 1 x 1200 @ 1 ohm
1 x 250 @ 4 ohms / 1 x 400 @ 2 ohms / 1 x 600 @ 1 ohm
2 x 125 @ 4 ohms / 2 x 200 @ 2 ohms / 1 x 400 @ 4 ohms
2 x 100 @ 4 ohms / 2 x 180 @ 2 ohms / 1 x 300 @ 4 ohms
1 x 125 @ 4 ohms / 1 x 225 @ 2 ohms / 1 x 300 @ 1 ohm
2 x 75 @ 4 ohms / 2 x 130 @ 2 ohms / 1 x 225 @ 4 ohms

HCCA-D2400

425 watts
2 x 50 @ 4 ohms / 2 x 100 @ 2 ohms / 1 x 200 @ 4 ohms
4 x 65 @ 4 ohms / 4 x 100 @ 2 ohms / 2 x 200 @ 4 ohms
4 x 50 @ 4 ohms / 4 x 75 @ 2 ohms / 2 x 150 @ 4 ohms

HP-4800

DIRECTED IS A PROUD MEMBER OF

65 watts

W W W.ORIONCAR AUDIO.COM
Designed and Engineered in USA by

HP-2800

HP-RB1 Remote Bass Control
_ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
2006 Directed Electronics. All Rights Reserved. 903F 04.06

Search

Collections

Journals

Contact us

My IOPscience

Retrieving physical conditions from interstellar H2 emission lines: a non linear fitting technique
This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 J. Phys.: Conf. Ser. (http://iopscience.iop.org/1742-6596/6/1/022) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 91.121.81.87 The article was downloaded on 09/06/2011 at 04:03
Please note that terms and conditions apply.
Institute of Physics Publishing doi:10.1088/1742-6596/6/1/022
Journal of Physics: Conference Series 6 (2005) 191196 Light, Dust and Chemical Evolution
Retrieving physical conditions from interstellar H2 emission lines: a non linear tting technique
Silvia Casu and Cesare Cecchi-Pestellini
INAF - Osservatorio Astronomico di Cagliari-AstroChemistry Group-Strada N.54, Loc. Poggio dei Pini, I-09012 Capoterra (CA) E-mail: silvia@ca.astro.it Abstract. The importance of the formation pumping on the rovibrational level distribution of H2 is revisited. A detailed comparison of dierent formation mechanisms on dust surfaces and in the gas-phase is carried out, and it is found that dust surface formation dominates the formation pumping. It is shown that formation pumping in a cold gas can mimic the excitation conditions found in hotter regions. The presence of a signicant fraction of molecular hydrogen in very high rotational levels observed towards OMC-1 Peak 1 is explained by means of pumping by newly formed H2 molecules and does not require high temperature gas.
1. Introduction. Dust grains conventionally provide a surface for the formation of H2 from atomic hydrogen [11]. Although there is a general agreement about the process, the actual mechanism is not understood and the internal energy distribution of the nascent hydrogen molecule is unknown. Presumably some fraction of the bond energy, 4.476 eV, of H2 is retained and subsequently redistributed as the H2 molecule undergoes collisions in the interstellar gas. There have been experimental attempts to measure the degree of vibrational excitation of H2 desorbed from surfaces [10], which support the prediction that a signicant fraction of the newly formed H2 is in vibrational and rotational excited levels of the ground electronic state. Classical molecular dynamics and fully quantum mechanical calculations have been carried out for H2 formation on surfaces considered analogs of interstellar dust [3,2,17,24,5], but the results have been quite dierent particularly in the predicted vibrational distribution. In the modelling exercise, various assumptions have been made. Black & Dalgarno (1976)[1] proposed that the H2 formation energy is equipartitioned among the internal energy of the molecule, the kinetic energy of the molecule, and the internal energy of the grain lattice. They further assumed that the 1.5 eV of H2 internal energy is distributed statistically among the rovibrational levels. Le Bourlot et al (1995)[13] considered the formation of H2 in its highest vibrational level, v = 14 close to the dissociation threshold, with J = 2 and 3, weighted by the nuclear spin statistics. No energy is transferred to translation or to dust lattice modes. Duley & Williams (1986)[8] suggested a mechanism which diers from previous proposals in the method of stabilization of the reacting complex. The stabilization energy ( 0.4 eV) is transferred to a surface band, whose energy is that of the OH stretching vibration. The model predicts that the H2 molecule on formation is ejected into the gas vibrationally excited (v 7) but rotationally cool (J = 0, 1). Draine & Bertoldi (1986)[7] proposed a rovibrational distribution function that does not include the rotational degeneracy factor 2J + 1 but includes a factor 1 + v. The formation temperature is Tf = 50, 000 K, the ortho-to-para ratio is 2.78, the mean vibrational

2005 IOP Publishing Ltd 191
and rotational levels are 5.3 and 8.7, respectively. The deviation from the statistical thermal distribution function has been introduced to enhance the populations of high vibrational states relative to high rotational states. Detailed quantum mechanical calculations have shown that much of the H2 should be produced in an excited state, with rovibrational and translational energy of the order of 1 eV [9,16]. Takahashi & Uehara (2001)[23] investigated the eects of formation pumping on the infrared H2 emission spectra produced in a collisionless gas. These authors constructed formation pumping models for hydrogen molecules newly formed on icy mantles, carbonaceous and silicate dust, based on classical and quantum theoretical studies of molecular dynamics [17,22,9,16]. A more detailed model was presented by Tin et al. (2003) [26], that predicted H2 rovibrational e emission line intensities for representative points in diuse and dark interstellar clouds. Clear spectral signatures of H2 formation on dust are evident in the resulting spectra. Using ISO/SWS [20] obtained near- and mid-infrared spectra towards OMC-1 Peak 1, which contain a number of emission and absorption features, dominated by 56 H2 rovibrational and pure rotational lines. Data analysis provide information on the average gas excitation over an unprecedented range (from Tex = 600 K for the lowest rotational and vibrational states up to Tex 3000 K at level energies larger than EvJ /k > 14, 000 K). Although existing C-shock models have been able to provide results in excellent agreement with observational data up to level energies EvJ /k 40, 000 K [14], they fail by a factor of ve to reproduce the highest observed level (v, J = (0, 27)). Rosenthal, Bertoldi & Drapatz (2000) [20] suggested that a dierent mechanism (e.g. gas-phase routes) might be populating this level and possibly other high levels. In this work we revisit the contribution of H2 formation pumping to the population of the high-energy levels. We do not try to constrain a shock model of the emitting region observed by Rosenthal, Bertoldi & Drapatz (2000) [20], since this task is accomplished by existing Cshock models [14]. Instead, we present a detailed analysis of the possible role played by the H2 formation process in the shaping of the very high energy level distribution. 2. The model 2.1. Associative detachment We constructed models of thermally excited H2 , in which the H2 level populations result from formation pumping, radiative decay, collisional excitation and de-excitation. The approach is similar in many respects to those developed by Sternberg & Dalgarno (1989) [21] and Draine & Bertoldi (1996) [7]. The details of the model are reported in [4]. The presence of large column densities of H2 in low levels of excitation suggests the cohexistence of two dierent emitting regions in the ISO/SWS eld of view. We summarize the characteristics of the shocked region by two layers at dierent kinetic temperatures and densities and adopted the set of physical parameters suggested by Rosenthal, Bertoldi & Drapatz (2000) [20] (see also [4]). Following the suggestion by Rosenthal, Bertoldi & Drapatz (2000) [20], we rstly explore the possibility that gas-phase formation pumping might be ecient in populating highly excited rovibrational levels. In fact, although the recombination of H atoms absorbed onto grains produces much more H2 than any gas-phase process, the associative detachment mechanism involving atomic hydrogen and the negative ion H can be ecient under particular conditions [15,6]. In particular, the associative detachment reaction produces H2 molecules preferentially in highly excited rovibrational levels, which then cascade towards the ground vibrational state by quadrupole radiative transitions. We hence include in the formation rate the additional contribution of the associative detachment channel. The results of our computations show that the inclusion of the associative detachment process in the molecular pumping does not alleviate the problem posed by the existence of a high degree

Figure 1. Ratio of gas-phase and surface formation rates of H2. The ionization fraction is xe = 103. (a) Tk = 200 K. (b) Tk = 800 K. of excitation [4]. In Fig.1a,b we show the ratios of gas-phase and surface formation rates of H2 (vJ n /RvJ nH ) for individual energy levels for the two layers. It is evident that gas-phase formation is much less ecient than surface catalysis which dominates the production pumping of newly formed molecules. 2.2. Surface pumping models Recently, Meyer etal. (2001) [16] studied the associative desorption of H2 on a graphite surface via an Eley-Reidel mechanism under conditions relevant to the interstellar medium. In the Eley-Reidel mechanism the second incident gas-phase H atom collides with the rst H atom chemisorbed on the surface. Meyer et al. (2001) [16] used a time-dependent wave packet method and a newly developed potential, treating three degrees of freedom quantum mechanically. The product H2 molecule appears less vibrationally excited than supposed previously on the basis of two-dimensional simulations. Most molecules have v 2, but newly formed molecules have signicant rotational excitation that peaks at about J = 15. The fraction of bond energy retained as internal energy of the molecule is approximately one third, and up 40-50% of the total energy can appear as translational energy. The remaining fraction is taken up as dust lattice excitation. Thus, surface formation pumping may be important in populating high rotational states of the ground vibrational level. This possibility is explored in this section. We present results for a number of formation pumping models and some thermal proles for the two gas layers mimicking the emitting region towards Orion OMC-1 Peak 1. In producing best-t results we exploit a non-linear tting technique, i.e. the Levenberg-Marquard method through the minimization of a 2 merit function with respect to free parameters in their acceptable ranges (see [4,18,19] for details) We consider formation pumping models in which the acquired internal energy, Tf , is statistically distributed among the energy levels (model A: f1 = 2J + 1, f2 = EvJ /Tf ). To enhance the populations of high-v states with respect to high-J states we consider also formation pumping functions with f1 = v + 1 (model B). Thus,

Figure 2. Upper panels: excitations diagrams for class B (left side) and class C best-t models (right side). Model column densities ( ) are compared with observational data ( ). Lower panels: Residuals normalised to the observational data. the models proposed by Black & Dalgarno (1976) is a class A model in the case of equipartition of energy between internal energy of the product molecule, translational degrees of freedom and dust lattice modes, while a class B model with Tf = 50, 000 K corresponds to the pumping prole suggested by Draine & Bertoldi (1996) [7]. Finally, we include in the calculations the two vibration-rotation distributions of Takahashi & Uehara [23] for H2 newly formed on icy mantles, carbonaceous dust, and silicate dust (models C). The formation temperatures are taken in the range 5, 000 Tf 50, 000 K, although very high formation temperatures are unlikely because some fraction of the formation energy is lost to overcome the grain surface potential and some possibly goes into translational kinetic energy. Gas kinetic temperatures are Tk = 100, 200 and 300 K for the cooler slab, while in the warmer region Tk = 600, 800 K. We consider L = 8 adjustable parameters, i.e. the set R, nH , 12 , and N2 , for each gas layers. In order to obtain the best model description of the Orion OMC-1 peak 1 observational data 2 [20] we selected models having a normalized 2 = 2 /N0,105 (where N0,3 is the column n density of the level v, J = (0, 3)), and plausible physical parameters. The more likely thermal congurations found with this analysis are Tk = 100 and 600 K, and Tk = 100 and 800 K. Under these circumstances, at least for formation pumping models of type A and B, the H2 formation rate R is always slower in the warmer slab than in the colder one. Figs.2(a-b) show the excitation diagrams for the selected best class B and class C formation pumping models. In the lower panels, the residuals of column densities RvJ = |NvJ (mod) NvJ (obs)|/NvJ (obs) are displayed. These models provide results in overall reasonably good agreement with data. They fail in reproducing very high pure rotational states and show subthermal excitation of levels in excited vibrational manifolds. In Fig.3 we show the excitation diagram for the selected best model, which is a class A model with Tf = 15, 000 K. With the exception of energy levels of excited vibrational
Figure 3. Upper panel : excitation diagram for the selected best model. Model column densities ( and ) are compared with observational data ( ). Down-pointing arrows indicate upper limits. Dots represent C-shock model results given in Le Bourlot et al. (2002) [14]. Lower panel : normalized residual. : pure rotational levels; : upper limits; + : levels of excited vibrational manifolds. manifolds (in particular v = 1), that are underpopulated with respect to the observational values, the agreement between modelled and observational data is in general satisfactory (cf lower panel in Fig.3). The observational errors are not shown in Fig.3, except than in the v, J = (0, 27) case, since they are of the order of the circle radius. It is evident that the highest rotational states detected, v, J = (0, 23) and (0, 27), are perfectly reproduced. The population of these states does not require high temperature gas and it is a clear signature of the surface formation pumping. No model with a dierent formation pumping function can populate eectively these states. Moreover, only class A models with formation temperatures in the range 10, 000 K Tf 20, 000 K can accomplish this task. In Fig.3 we have also plotted the upper limits to the column densities of other very high energy rotational levels given in Rosenthal, Bertoldi & Drapatz (2000) [20] together with the results of a C-shock model of this region presented by Le Bourlot et al. (2002) [14]. It is interesting to note that these upper limits are suggestive of the existence of an high excitation tail (Tex 3, 000 K) in the OMC-1 H2 excitation diagram. These peculiar excitation conditions are present in our model results shown in Fig.3. Finally, we would like to briey discuss the osets between the v = 0 and v = 1 populations, which is also found in Rosenthal, Bertoldi & Drapatz (2000) [20], but which does not occur in the observations. In a shock wave the sudden rise of translational temperature is not immediately

followed by an increase in the vibrational temperature, whose relaxation time is typically longer. Vibrational non-equilibrium therefore may arise due to rapid quasi-resonant vibration-vibration energy transfer between molecules. We have attempted to empirically simulate vibrational non-equilibrium inserting a damping factor in the de-excitation rates of energy levels in excited vibrational states. Although we obtained a better agreement with observational data, the overall description of v > 0 populations is not satisfactory and it requires a detailed treatment, e.g. by direct Monte Carlo simulation. Interesting enough, the damping factor does not produce appreciable modications in the distribution of pure rotational levels. 3. Conclusions The results of the present calculations suggest that H2 formation on dust grain surfaces constitutes an important pumping channel and should be included in the modelling procedure. In particular, in the cold gas surface formation pumping dominates the populations of level J 20. The distribution prole of very high energy levels is strongly aected by the assumed surface pumping function and depends particularly on the formation temperature. The large unexpected population of the energy level v, J = (0, 27) is a clear signature of the surface formation process. The population of the energy level v, J = (0, 27), and possibly those of other very high energy states, scales linearly with both the total cold H2 column density and the total H2 surface formation rate R. It is not clear how to discriminate among formation mechanisms, e.g. between Eley-Reidel and Langmuir-Inshelwood schemes, and among suggested surface pumping functions (excited vibrational levels are probably out of equilibrium). However, the (relatively) unbiased adopted tting technique suggests that the H2 formation energy is equipartitioned among the internal energy of the molecule, the kinetic energy of the molecule, and the internal energy of the grain lattice. References
[1] Black J.H., Dalgarno A., 1976, ApJ, 132, 142 [2] Buch V., Devlin J.P., 1993, J. Chem. Phys., 98, 4195 [3] Buch V., Zhang Q., 1991, ApJ, 379, 647 [4] Casu S., Cecchi-Pestellini C., submitted to MNRAS [5] Cazaux S., Tielens A.G.G.M., 2004, ApJ, 604, 222 [6] Cecchi-Pestellini C., Dalgarno A., 1993, ApJ, 413, 611 [7] Draine B.T., Bertoldi F., 1996, ApJ, 468, 269 [8] Duley W.W., Williams D.A., 1986, MNRAS, 223, 177 [9] Farebrother A.J., Meijer A.J.H.M., Clary D.C., Fisher A., 2000, Chem. Phys. Lett., 319, 303 [10] Gough S., Schermann C., Pichou F., Landau M., Cadez I., Hall R. I., 1995, A&A, 305, 687 [11] Hollenbach D.R., Salpeter E.E., 1970, J. Chem. Phys., 53, 79 [12] Launay J.M., Le Dourneuf M., Zeippen C.J., 1991, A&A, 252, 842 [13] Le Bourlot J., Pineau des Forts G., Roue E., Dalgarno A., Gredel R., 1995, ApJ, 449, 178 e [14] Le Bourlot J., Pineau des Forts G., Flower D.R., Cabrit S., 2002, MNRAS, 332, 985 e [15] Lepp S., Stancil P.C., Dalgarno A., 2002, J. Phys. B., 35, R57 [16] Meijer A.J.H.M., Forebrother A.J., Clary D.C., Fisher A., 2001, J. Phys. Chem, 105, 2173 [17] Parneix P., Brechignac Ph., 1998, A&A, 334, 363 [18] Press W.H., Teukolsky S.A., Wetterling W.T., Flannery B.P., 1992, Numerical Recipes, (Cambridge: Cambridge University Press) [19] Rodgers C.D., 2000, Inverse Methods for Atmospheric Sounding (Singapore: World Scientic) [20] Rosenthal D., Bertoldi F., Drapatz S., 2000, A&A, 356, 705 [21] Sternberg A., Dalgarno A., 1989, ApJ, 338, 197 [22] Takahashi J., Masuda K, Nagaoka M., 1999, ApJ, 520, 724 [23] Takahashi J., Uehara H., 2001, ApJ, 561, 843 [24] Takahashi J., Williams D.A., 2000, MNRAS, 314, 273 [25] Tin S., Lepp S., Gredel R., Dalgarno A., 1997, ApJ, 481, 282 e [26] Tin S., Williams D.A., Clary D.C., Forebrother A.J., Fisher A.J., Meijer A.J.H.M., Rawlings J.M.C., Davis e C.J., 2003, Ap&SS, 288, 377