Shock Waves (1998) 8: 311 319
Shock reaction of hexane at 77, 193, and 273 K
with special reference to shock pressure
K. Mimura1, M. Kato2, M. Ohashi3, R. Sugisaki4
1
Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-01, Japan
2
Center for Advanced Spacecraft Technology, The Institute of Space and Astronomical Science Sagamihara, Kanagawa 229,
Japan
3
Department of Chemistry Kanagawa University, Hiratsuka, 259-12, Japan
4
Department of Teacher Education, Meijo University, Nagoya 468, Japan
Received 12 September 1997 / Accepted 14 October 1997
Abstract. Shock waves generated by projectile impacts were transmitted into hexane and the shocked
hexane was analyzed by TCD-GC, FID-GC, GCMS, and FABMS for produced aliphatic hydrocarbons.
The projectile length and its velocity were varied from 10 to 40 mm and from 220 to 1040 m/s, respectively.
The initial temperature of the hexane was 77, 193 and 273 K. The major products detected throughout
the reactions were hydrogen, light alkanes from C1 to C4, and light alkenes from C2 to C3. The minor
products were heavy alkanes from C8 to C12 and soot-like materials. Experiments with varied projectile
length revealed that the shock reaction occurred only while the shock wave was transmitted through hexane
(about 10-6 seconds). This short reaction time may be responsible for a lower yield of branched products
in the shock reaction compared with yield produced by hexane pyrolysis in previous studies. In the shock
reaction of hexane, the dehydrogenation was one of the important reactions and the recombination of hexyl
radicals might play a role in the formation of n-C12. Experiments with varied initial temperature suggested
that the molar yield of products depends not on the shock temperature but on the shock pressure, and that
the reaction mechanisms for solid hexane and for liquid hexane are not identical. As the shock pressure
increased, the relative yield of heavy products increased while that of light products decreased. This could
be interpreted mainly by considering the activation volumes of the reaction involved.
Key words: Hexane, Shock reaction, Dehydrogenation, Shock pressure, Reactant form, Activation volume
1 Introduction ditions of high pressure and temperature for extraordi-
narily short time periods behave in a particular way; they
must be subjected to a unique and unknown chemical pro-
Shock-wave techniques offer a means of generating ex-
cess. With this expectation, we applied the new system
tremely high pressures and temperatures that are difficult
to synthesize organic materials and to examine reaction
to achieve by normal static experimental methods. These
mechanisms in the process. In the experiments, some hy-
techniques have been applied to study properties of or-
drocarbon gases were easily synthesized from a mixture
ganic and inorganic materials (Ree 1979), and to synthe-
of CO and H2 (Sugisaki et al. 1994) and many kinds of
size some materials (Titov et al. 1989). Researchers have
molecules comprising polycyclic aromatic hydrocarbons
used several types of shock apparatus (Dick 1970; Nellis
were produced from benzene (Mimura et al. 1994; Mimura
1983; Hidaka et al. 1989), but few methods allowed for the
1995; Mimura et al. 1995). In the latter experiment, we
collection of the materials produced without contamina-
concluded that a concerted cycloaddition reaction con-
tion. Recently, we developed a simplified system for the
trolled by the Woodward Hoffmann rules is responsible
shock technique, which can be applied to any form of ma-
for the formation of some products in the shock reaction
terial and which permits us to examine shocked products
(Mimura 1995; Mimura et al. 1995). Thus, experiments
without contamination (Sugisaki et al. 1994; Mimura et
using this new system may be open to a new field of chem-
al. 1994).
istry.
A material is in a high-pressure, high-temperature
state when a shock wave is transmitted through it; the In the present study, we shocked hexane under vari-
state returns to the initial state immediately after the ous conditions, such as initial temperatures, the projectiles
wave has passed. Materials subjected to the extreme con- lengths and velocities, and analyzed the shocked hexane
312 K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure
to identify what kinds of molecules were produced by the Table 1. Shock periods and pressures of all projectile veloc-
process. The various lengths of the projectiles resulted in ities calculated for three projectile lengths and three initial
temperatures
different shock periods. Varying the initial temperatures
of hexane just before the shock reaction brought about dif-
Projectile Initial Projectile Shock Shock
ferent densities and forms of hexane, giving rise to shock-
lenght temperature velocity period pressure
pressure changes. Experimental results under various con-
(mm) (K) (m/s) (µs) (Kb)
ditions furnished basic data concerning the shock reaction
of hexane, which were compared with those of hexane py- 10 77 398 3.57 2.16
rolysis reported in previous studies (Imbert and Marshall 10 77 473 3.55 2.58
10 77 543 3.52 3.02
1987; Dominé 1989).
10 77 649 3.49 3.68
10 77 833 3.44 4.88
10 77 950 3.41 5.67
2 Experimental section
10 77 1020 3.40 6.16
10 77 1040 3.39 6.30
Our previous studies described the apparatus and pro-
10 193 306 3.60 1.15
cedures for the experiment (Sugisaki et al. 1994; Mimura
10 193 450 3.55 1.76
1995). In this study, we used cylindrical aluminum projec- 10 193 632 3.50 2.58
tiles (15 mm in diameter and 10, 20 and 40 mm long) with
10 193 740 3.47 3.09
initial temperatures of 77, 193 and 273 K. The experiments 10 193 871 3.43 3.75
were carried out under the two following conditions. 10 193 950 3.41 4.17
10 193 1010 3.40 4.49
10 193 1040 3.39 4.65
10 273 411 3.57 1.14
2.1 Various projectile lengths (10, 20 and 40 mm)
10 273 602 3.51 1.77
at a fixed initial temperature (273 K)
10 273 740 3.47 2.26
10 273 806 3.45 2.51
The initial substance was pure hexane distilled from a
10 273 862 3.44 2.73
commercial reagent of the highest quality. A stainless-steel
10 273 999 3.40 3.28
container cooled by a mixture of ice and water (273 K) was
10 273 1032 3.39 3.42
filled with the hexane. No air space was present in the
20 273 280 7.22 0.74
container. When a projectile from a vertical powder gun
20 273 337 7.18 0.91
struck the lid of the container, a shock wave was transmit-
20 273 420 7.13 1.17
ted into the hexane. The projectile velocities ranged from
20 273 552 7.04 1.60
411 to 1032 m/s, 280 to 757 m/s, and 220 to 523 m/s for
20 273 598 7.02 1.75
projectile lengths of 10, 20 and 40 mm, respectively. Above 20 273 640 6.99 1.90
these upper velocity ranges, the container was destroyed 20 273 757 6.93 2.33
and products were lost. The projectile velocity was mea- 40 273 220 14.5 0.57
40 273 285 14.4 0.76
sured by the conventional method of recording the flight
40 273 342 14.4 0.93
time difference between two laser beams with a digitizing
40 273 396 14.3 1.09
oscilloscope.
40 273 458 14.2 1.29
40 273 523 14.1 1.50
2.2 Various initial temperatures (77, 193 and 273 K)
for a fixed projectile length (10 mm)
by FID-GC, GCMS (Shimadzu QP2000). Soot-like mate-
rials were analyzed by FABMS.
The container of hexane was cooled with liquid nitrogen
(77 K), with a mixture of dry ice and ethanol (193 K), and The analytical conditions were as follows. The TCD-
with a mixture of ice and water (273 K). A shock wave GC was fixed with a 3 m×3 mm column packed with a
was transmitted into the hexane by a 10 mm projectile molecular sieve 5A (60/80 mesh). The FID-GC for de-
traveling at velocities ranging from 306 to 1040 m/s. termination of LHCs was fixed with a 3 m×3 mm column
The shocked hexane recovered from the container was packed with a unipak S (100%SiO2, 100/150 mesh). The
directly injected into a GC to determine dissolved H2 column and injection temperatures were adjusted to 50ć%C
and low-molecular-weight hydrocarbons (LHCs). Hydro- and 150ć%C, respectively. The GCMS and FID-GC for de-
gen and LHCs were analyzed by TCD-GC (Ohkura 802) termination of HHCs were fitted with a 60 m×0.25 mm
and FID-GC (Ohkura 202), respectively. The shocked hex- fused silica capillary column coated with a 0.25 µm layer
ane was subsequently charged with an internal standard of TC-1 (100% dimethyl polysiloxane). The column tem-
and concentrated by a rotary evaporator. 3-methyl un- perature-program was 60ć%Cto 250ć%Cat 4ć%C/min. The in-
decane that was not contained in the sample was used jection temperature was adjusted to 250ć%C. FABMS were
as the internal standard. High-molecular-weight hydrocar- recorded on a Finnigan MAT TSQ 700 triple-stage
bons (HHCs) in the concentrated solution were analyzed quadrupole mass spectrometer equipped with an Ion Tech
K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure 313
Fig. 1a,b. Representative gas chromatogram of products from
shocked hexane for a 10-mm projectile, 273 K, and a projectile
velocity of 999 m/s. a LHCs (low-molecular-weight hydrocar-
bons), peak numbers 1, 2, 3, 4, 5, and 6 show CH4, C2H6,
C2H4, C3H8, n-C4H10, and C3H6, respectively. b HHCs (high-
molecular-weight hydrocarbons), peak numbers 1, 2, 3, and
4 show C9-isomers, C10-isomers, C11-isomer, and C12-isomer,
respectively
FAB gun. A xenon beam with an energy of 8 keV and
glycerol as the matrix was used.
The identification and determination of products were
as follows. Hydrogen and LHCs were identified by com-
parison with the retention times of authentic compounds
on the chromatograms. These quantities were estimated
from peak areas on the chromatogram by comparison with
those of authentic compounds. HHCs were identified by
comparison with retention times and fragmental patterns Fig. 2a,b. Molar yield (n mol of product / initial mol of hex-
ane) of products versus projectile velocity for 10-mm projectile
of authentic compounds. The quantities were determined
and 273 K. a H2 and LHCs. b HHCs
by the same method for H2 and LHCs.
Shock pressures caused by the transmission of the
shock wave into the hexane were calculated (Table 1) by
the impedance matching technique (Meyers 1994) on the shocked hexane were H2, LHCs consisting of
basis of the bulk modulus (Walsh and Rice 1957), density alkanes from C1 to C4 and of alkenes from C2 to C3,
(Rossini et al. 1953) and the sound velocity of hexane at and HHCs consisting of some isomers of saturated C8,
the initial temperature; the sound velocity was adopted C9, C10, C11, and C12. The amounts of isomers, except
from data measured by the ultrasonic pulse transmission for normal alkanes, were not determined, because no au-
method (Yamashita et al. 1994). In calculating the pres- thentic standard compounds for these isomers were avail-
sure, we assumed that the bulk modulus of hexane was able. The shocked hexane contained soot-like materials
constant. The shock period was estimated to be approxi- which were not carbon clusters. Acetylene and isobutane
mately twice the travel time of the shock wave through the were ambiguously detected in several samples. Represen-
projectile (Table 1), because the shock wave was reflected tative gas chromatograms of LHCs and HHCs are shown in
from the back surface of the projectile and returned into Fig. 1. The relationships of molar yields (n mol of products
the target as a release wave. The shock temperature can / initial mol of hexane) in shocked samples versus projec-
be calculated on the basis of the relative volume (the spe- tile velocities are illustrated in Figs. 2 to Fig. 6, in which
cific volume behind the shock front divided by the specific the initial temperatures and projectile lengths are indi-
volume ahead the shock front), the Grüneisen gamma, and cated. The yield below 50 n mol/mol for H2 and LHCs, and
initial temperature of the material. However, we were un- 0.5 n mol/mol for HHCs cannot be determined.
able to estimate the shock temperature because we did
As a representative result, Fig. 2 shows the relationship
not have the Grüneisen gamma for hexane.
between the molar yield of each product and the projec-
tile velocity for the 10-mm projectile length and an initial
temperature of 273 K. As the projectile velocity increased,
each molar yield increased. The molar yields of the prod-
3 Results
ucts decreased with increasing carbon numbers. Hydrogen
Many kinds of molecules were produced from pure hexane (and CH4) was one of the major products. Hydrogen and
under different conditions. The molecules detected for the LHCs were produced much more than HHCs were. Unsat-
314 K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure
Fig. 4a,b. Total molar yield of some products versus projectile
Fig. 3a,b. Total molar yield of some products versus projectile
velocity, for 10-mm projectile and three initial temperatures.
velocity, for three projectile lengths and 273 K. a H2 and LHCs.
a H2 and LHCs. b HHCs
b HHCs. HHCs in the experiment at 20 mm, 273 K and 280 m/s
were not determined
were the lowest. At a higher range of projectile veloci-
urated hydrocarbons were produced more than saturated
ties, the yield differences between 77 K and 273 K became
ones with respect to the same carbon number, namely
smaller as the carbon number contained in LHCs increased
C2H4 > C2H6 and C3H6 > C3H8.
(Fig. 5). In particular, the yield for n-C4 at 77 K exceeded
the yield at 273 K, and approached the yield at 193 K
(Fig. 5d). This tendency was strengthened in HHCs: the
3.1 Varied projectile length experiment at 273 K
yield of HHCs at 77 K was larger than that at 273 K and
was close to that of 193 K (Fig. 4b). Averages and their
Total molar yields of H2 and LHCs, and those of HHCs
standard deviations for the relative yield (molar yield of
were plotted against projectile velocities for each projectile
a particular product divided by the total molar yield of
length in Fig. 3. Molar yields of all products (H2, LHCs,
products) of each product obtained with the 10-mm pro-
and HHCs) increased with increasing projectile lengths
jectile at all velocities were calculated for the three initial
and velocities. The mutual ratios of total yields at 10, 20
temperatures (Table 2). The relative molar yields of H2
and 40 mm were about 1:2:4.
and C2H4 decreased with decreasing temperature, while
those of other products increased with decreasing temper-
ature.
3.2 Varied initial temperature experiment
at 10 mm length
4 Discussion
The relationships between the total yields of the prod-
ucts and the projectile velocity at various initial tempera-
tures and for the 10-mm projectile are shown in Fig. 4. For The pyrolysis of hydrocarbons has been investigated by
a fixed projectile velocity the total yields at 193 K were numerous authors (Konar et al. 1968; Baronnet et al. 1971;
higher than those at 77 K and 273 K, except for HHCs Bull et al. 1975) and the pyrolysis of hexane in particular
at 1040 m/s. The total yields of H2 and LHCs at 77 K was studied by Imbert and Marshall (1987) and Dominé
K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure 315
Table 2. Averages and their standard deviations for relative yield (molar yield of some product/total molar yield of
products) of each product obtained by 10 mm projectile at all velocities for the three initial temperatures
Initial H2(×10-1) CH4(×10-1) C2H6(×10-2) C2H4(×10-1) C3H8(×10-2) C3H6(×10-2)
temperature av." s.d." av. s.d. av. s.d. av. s.d. av. s.d. av. s.d.
77 K 2.45 0.22 3.10 0.56 12.4 0.47 1.38 0.30 6.20 1.55 8.50 1.83
193 K 3.31 0.57 2.88 0.37 9.29 1.22 1.48 0.24 4.20 1.08 7.71 0.91
273 K 3.58 0.36 2.41 0.27 8.51 1.02 1.82 0.14 4.15 0.99 7.47 1.14
Initial n-C4H10(×10-2) n-C8(×10-4) n-C9(×10-4) n-C10(×10-4) n-C11(×10-5) n-C12(×10-5)
temperature av. s.d. av. s.d. av. s.d. av. s.d. av. s.d. av. s.d.
77 K 3.12 0.84 17.3 7.22 10.2 4.06 7.49 1.97 22.4 6.16 20.1 5.55
193 K 1.97 0.35 6.56 2.10 3.86 1.26 2.82 0.68 8.43 2.60 8.89 2.32
273 K 1.67 0.50 6.30 1.46 3.70 0.85 2.82 0.23 7.63 1.23 7.19 1.06
* Av. and s.d. are abbreviations for average and standard deviation, respectively.
Fig. 5a d. Molar yield of light saturated
hydrocarbons versus projectile velocity for
10-mm projectile and three initial tem-
peratures. a CH4. b C2H6. c C3H8. d n-
C4H10
(1989). Mimura (1995) inferred from his experimental re- features of the present study are as follows. (1) The shock
sults that the shock reaction of benzene corresponds to wave interacts with hexane only during an extremely short
pyrolysis of the initial substance at high temperatures period ranging from about 3.5 to 14 µs; (2) the shock wave
caused by a shock wave. However, the experimental con- forces hexane to undergo high pressures of 1.7 to 6.3 Kb;
dition of the shock reaction was markedly different from and (3) different forms of hexane (liquid and solid) can
that in the current pyrolysis experiments of hexane; the be used as the initial substance. These features necessar-
reaction time in the latter was longer than 10 seconds ily cause some qualitative and quantitative differences in
and the pressure was lower than 1 Kb, although the pres- the experimental result between other studies of hexane
sure in Dominé (1989) amounted to 15.6 Kb. The notable pyrolysis and the present study.
316 K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure
3.5, 7.0 and 14 µs, respectively (Table 1). Total yield rates
(total molar yield/shock period) of the products for each
projectile velocity are plotted on a common curve inde-
pendent of projectile lengths (Fig. 6), although total yields
of products for the three projectile types cluster around
the three respective curves (Fig. 3). Furthermore, com-
positions of products at each projectile length did not
change much through the experimental runs. These re-
sults demonstrate that the molar yield in shock reaction
is controlled by the shock period at the same projectile
velocity and initial temperature, and that the shock reac-
tion proceeds during only the period at which the shock
wave interacts with hexane.
4.2 Probable reaction mechanism in the shock reaction
What controls the composition of products in the shock
process? Hydrogen are CH4 are the major products in the
shock reaction. This experimental result is uniquely dif-
ferent from that of hexane pyrolysis where H2 is a minor
product (Imbert and Marshall 1987). Molar ratios of hy-
drogen to carbon (H/C) in products are about 3.3 at ini-
tial temperatures of 193 and 273 K, and about 3.1 at 77 K.
Although yields of HHCs isomers except for those with a
normal chain were excluded from the calculation of H/C
ratio, these isomers in a small amount do not spoil the cal-
culation. These H/C ratios in the products are different
from that in hexane (2.7). The shocked hexane contains
soot-like materials that are not soluble in organic solvents
Fig. 6a,b. Total molar yield rate (total molar yield/shock
such as hexane and benzene. They are probably carbona-
period) of some products versus projectile velocity for three
ceous materials poor in hydrogen. These facts show that
projectile lengths and 273 K. a H2 and LHCs. b HHCs
the dehydrogenation from hexane plays a major role in
the shock reaction, and forms the excess free-hydrogen
and the compensatory soot-like materials deficient in H.
In these previous studies, the mechanism of hexane py-
We may compare the shock reaction with the collision-
rolysis has been interpreted as a free-radical reaction. In
induced decomposition (CID), because both reactions are
the shock reaction, three variables, namely shock temper-
characterized by the production of H2 and by the con-
ature, shock pressure, and shock period, may be counted
tribution of shock phenomenon. CID is a well-known re-
as the major factors controlling the reaction. For the in-
action in the field of mass spectrometry (Adams 1990;
spection of the reaction mechanism, at least two variables
Gross 1992). The fragmentation of saturated materials in
among the three should be fixed. In the present study,
CID can be explained by the mechanism involving 1,4-
however, the three variables cannot be fixed simultane-
elimination of H2 and CnH2n. Supposing that hexane re-
ously owing to the differences in the projectile velocity. In-
acts by 1,4-elimination, the reaction should produce H2,
evitably, we are obliged to discuss qualitatively the chem-
C2H2, C3H6, and 1-C4H8. These unsaturated materials
ical composition and molar yields of products under dif-
should secondarily produce several materials, mainly CH4
ferent experimental conditions in this paper.
and other unsaturated materials, by the decomposition,
the polymerization, and the reaction with hexane. As men-
tioned above, the production of H2, CH4, and unsaturated
4.1 Reaction time in the shock reaction
materials in the shock reaction is possibly attributed to
In order to examine reactions involved in the shock pro- 1,4-elimination of the CID-type reactions.
cess, we must first identify the period when the reac- Produced hydrocarbons with a branched chain do not
tion occurs, when the shock front meets the hexane, or overwhelm those with a normal chain in amounts (Fig. 1b).
when the shock wave is traveling through the hexane. It is Assuming that sensitivities in the analyses for hydrocar-
physically deduced that the shock period is controlled by bons of the same carbon number (n) remain identical, the
the projectile length if the physical property and velocity molar ratio of branched Cn/normal Cn can be calculated
of projectile are the same. According to the impedance from the peak areas on the gas chromatogram. The esti-
match method (Meyers 1994) shock periods for projec- mated values were less than 1.5. In contrast, the ratio was
tile lengths of 10, 20, and 40 mm were estimated at about more than 5 (4-methyl octane/n-nonane) in the pyrolysis
K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure 317
experiment by Dominé (1989). The pyrolysis that slug-
gishly proceeds under a high-pressure condition prefers
the formation of branched hydrocarbons to that of nor-
mal ones, probably because of the small molar volume of
the former. Thus, the present experiment demonstrates
that some mechanism different from that in pyrolysis is
involved in the shock process for an instant.
The molar yield of n-C12 is close to that of n-C11 in
spite of the result showing that molar yields of HHCs de-
crease with increasing carbon number (Fig. 2b). Suppose
that a reaction mechanism of HHCs formation is the addi-
tion of two different species. n-C11 should then be formed
mainly by the addition of C6H13 to C5H10, and n-C12
should be mainly formed by the addition of C8H17 to
C4H8, of C9H19 to C3H6, and/or of C10H21 to C2H4. In
the products, n-C11 >n-C12 because C6H13 is one of ma-
jor radicals but C8H17, C9H19, and C10H21 are secondary
and minor radicals. The experimental result n-C11 H" n-
C12, however, conflicts with the hypothesis. On the other
hand, suppose that the reaction mechanism is the recom-
bination. n-C12 should then be formed from C6H13 and
C6H13. The recombination should produce more n-C12
than the addition does because of the high abundance of
C6H13. The reaction mechanism, including the recombina-
tion and the addition, may explain the similar production
of n-C11 and n-C12 in the shock reaction of hexane.
4.3 Significance of shock pressure and reactant form
Fig. 7a,b. Total molar yield of products versus shock pressure
Hexane is in solid form at 77 K and in liquid form at 193
for 10-mm projectile and three initial temperatures. a H2 and
and 273 K. Table 2 shows that the averages of the rela-
LHCs. b HHCs
tive yield of each product at 193 K and 273 K are similar;
those at 77 K are conspicuously higher, with the excep-
products for solid hexane (77 K) are lower than those in
tion of H2 and C2H4. Although this cannot be explained
at this stage, it seems evident that the shock-derived re- liquid hexane (193 and 273 K) at each pressure (Fig. 7).
This result suggests that the form-transfer from liquid to
action partly depends on the form of the reactant.
solid promotes a cage effect retarding bimolecular reac-
In general, the decrease in the initial temperatures of
the initial substance enhances the shock pressure and at- tions by hindering the migration of reacting molecules or
radicals.
tenuates the shock temperature because of the change in
It is generally accepted that the pressure modifies the
physical properties for the initial substance at the same
projectile velocity, though the exact shock temperature rate constant in a reaction at a constant temperature. The
cannot be estimated in the present experiment. The cal- following equation may be applied to the shock reaction
culated-shock pressures for the projectile velocity at each because the difference in shock temperature can be ne-
initial temperature are shown in Table 1. Figure 4 shows glected in this study, as mentioned above.
that the total yields in the experiment at 193 K are higher
!
(" ln K/"P )T = -"V /RT , (1)
than those at 273 K, though the shock temperature in
the former experiment is lower than that in the latter at
!
the same projectile velocity. The shock pressure at 193 K, where K is the rate constant and "V is the activation
however, is higher than that at 273 K. It is suggested, volume defined by the transition-state theory and depends
therefore, that the shock reaction depends mainly on the on the type of reaction (Asano and Noble 1978). Because
!
pressure irrespective of the temperature within the range "V is approximately +10 cm3/mol for unimolar reac-
of the present experimental conditions. When the data tions, such as formations of H2 and LHCs, the rate con-
shown in Fig. 4 are plotted against shock pressure, the stant should decrease with increasing pressure. In con-
!
total yields at 193 and 273 K are commonly plotted on tract, "V is approximately -10 cm3/mol for bimolec-
a line whereas those at 77 K are on another different line ular reactions, such as formations of HHCs, whose rate
(Fig. 7). This shows that the form of hexane and the shock constants should increase with increasing pressure. It is
pressure play an important role in the process; an effect predicted from the evaluation of activation volumes that,
derived from shock temperatures may be insignificant and as the pressure increases, the total relative yield for H2
confined to the experimental error. The total yields of all and LHCs should decrease, while that for HHCs should
318 K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure
total relative yield of HHCs increases while that of H2 and
LHCs decreases, and shows that this tendency becomes
more striking for solids.
Acknowledgements. We thank Drs. W. Agena, N. Handa, H.
Iwamori, M. Kumazawa, T. Masuda, S. Murata, H. Nakata,
T. Torii, K. Yamamoto, and Y. Yamashita. This study was
supported by the Grant in Aid for Scientific Research, No.
08740426, from the Ministry of Education, Japan.
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Konar RS, Purnell JH, Quinn CP (1968) Self-inhibition and
ours. Figure 8 also shows that the reaction mechanism for
mechanism of iso-butane pyrolysis. Trans. Faraday Soc. 64:
the initial substance in solid form is different from that for
1319
liquid form. The shock reaction for the solid form favors
Meyers MA (1994) Dynamic Behavior of Materials. Wiley, New
the formation of HHCs in comparison with that of H2 and
York
LHCs.
Mimura K, Kato M, Handa N, Sugisaki R (1994) Shock syn-
thesis of polycyclic aromatic hydrocarbons from benzene:
Its role in astrophysical processes. Geophys. Res. Lett. 21:
2071
5 Conclusions
Mimura K (1995) Synthesis of polycyclic aromatic hydrocar-
bons from benzene by impact shock: Its reaction mech-
The experiment with varied projectile lengths showed that
anism and cosmochemical significance. Geochim. Cos-
the shock reaction proceeds only during the shock period.
mochim. Acta 59: 579
The shock reaction is characterized by the following strik-
Mimura K, Ohashi M, Sugisaki R (1995) Hydrocarbon gases
ing features: (1) H2 and CH4 are the major products,
and aromatic hydrocarbons produced by impact shock
(2) the yield of branched products is not much higher
from frozen benzene: Cosmochemical significance. Earth
than that of normal products. These features reveal the
Planet. Sci. Lett. 133: 265
uniqueness of the shock reaction occurring during a very
Nellis WJ (1983) Shock fluid at high densities and tempera-
short time. The experiment with varied initial tempera-
tures. Shock Wave in Condensed Matter 1983: Chapter II:
tures suggests that the shock pressure not the shock tem-
3
perature plays a major role in the shock reaction within
Ree FH (1979) Systematics of high-pressure and high-
the whole range of experimental conditions. This experi- temperature behavior of hydrocarbons. J. Chem. Phys. 70:
ment also shows that, with increasing shock pressure, the 974
K. Mimura et al.: Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure 319
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Carnegie, Attsburgh Yamashita Y, Kato M, Suzuki K, Iijima Y, Yoneda A (1994)
Sugisaki R, Mimura K, Kato M (1994) Shock synthesis of light Elastic and inelastic properties of non-water ice. Proc. 27th
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