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SCIENTIFIC ABSTRACT: We propose to use ISOCAM to obtain CVF spectra of the near and mid-IR emission (LW1 and LW2 CVF segments, complete spectrum at full sampling from 5 to 16.5 micron: 2*84 steps) for lines of sight representative of specific components of the interstellar medium in various radiation environments. These observations will permit to clarify the nature of the large molecules/small particles at the origin of the near and mid-IR emission, to measure their abundance and determine their contribution to the energy budget of interstellar matter. They are fundamental to analyse the emission of more complex pieces of interstellar medium in the Galactic plane or external galaxies. IRAS observations have shown that the abundance of small particles varies from cloud to cloud and within clouds on scales as small as 0.5 pc. To investigate the origin of these abundance variations and their effect on the physics of clouds (heating, ionization) we propose to map several nearby clouds in the LW2 and LW3 filters to study the distribution of the small particles on small scales (pfov 6") within clouds. These maps will enable us to investigate the effect of small particles on the physical conditions within clouds, and check if their formation is linked to gas phase or/and dust mantles chemistry. In this proposal emphasis is put on interstellar matter far-away from local heating sources, named hereafter general interstellar matter. OBSERVATION SUMMARY: I. CVF Spectra For the spectroscopic part of this proposal we selected regions characteristic of specific components of the ISM. The selected targets have relatively low brightness. A sufficient signal to noise will be achieved by averaging all pixels within the array. A pixel field of view of 12" will be used to minimize read noise.The spectra will cover the full spectra range of the CVF with the LW detector: 5.2 to 16 micron. The sensitivity of the SW channel is insufficient to extend the spectra to shorter wavelengths within a reasonable amount of time. Some of the selected lines of sight are in common with the dust proposal of the PHOT team (P.I.: D. Lemke). This is done on purpose to complement their spectra and check for instrumental problems by comparing overlapping parts. After averaging the camera pixels the mean ISM brightness is detected with a S/N ratio of at least 10 per resolution element. The accuracy of the spectra is likely to be limited by gain drifts through the observation. To be able to estimate this source of error and possibly to help us correct it each spectrum is done twice within the same observation: going up and down in wavelengths. The corresponding AOTs are concatenated. II. Mapping of Nearby Interstellar Clouds For mapping we selected the broad-band filters LW2 (5-8.5 micron) and LW3 (12-17 micron). We will use a pixel field of view of 6" for both filters. These choices coincide with that made to carry out an extended survey for young stellar objects in nearby molecular complexes. This coordinated choice avoids duplicating observations of the same objects. Only frames on cloud edges and cirrus at high latitude are necessary to complement their list of targets to give us a representative set for the present study. With respect to sensitivity the LW2 filter which includes the 6.2 and 7.7 C-C features and part of the 8.6 micron C-H feature is the best to use for mapping the emission from PAHs. Nothing is observationally known about spectral features beyond 12 micron. We expect that the long wavelength filter LW3 will measure a combination of emission by large PAHs and 3 dimensional particles. The maps are covered through a raster with a step of 1/2 or 1/4 of the camera field of view. The observing time on a given map position is 120 sec to be divided in 2 or 4 exposures with different camera poitings. On each pointing 4 images are taken to enable deglitching. For sensitivity calculation we used the IRAS 12 micron brightness and assumed a flat nu*Inu spectrum. The expected sensitivity for both the LW2 and LW3 filters correpsonds to a S/N ratio of 10 for a 12 micron brightness of 0.4 MJy/sr.with IRAS, In practice we achieve a brightness sensitivity comparable to that of IRAS for a spatial resolution of 6" instead of 4'. To reduce the overheads due to poiting, AOTs for the same source are concatenated within a limit on the total observing time of 3hrs. III. Far-IR Mapping Thanks to contribution from Jean-Loup Puget, and the PHOT, SOT and CAM teams a dominant fraction of the fields mapped with ISOCAM (within this proposal and that entitled Search for YSOs in Molecular clouds, P.I.: L. Nordh) will be mapped with PHOT at 90 and 200 micron. For this we use the C100 and C200 cameras. For C200 the Cross and In-scan steps are 180". For C100, Cross and In-scan steps are 92" and 135", respectively. The observing time per position is 16sec for C200 and 10sec for C100. The sources covered with CAM time are included in this proposal. To reduce the overheads due to pointing, AOTs for the same source are concatenated within a limit on the total observing time of 3hrs C