molecular beam pulsed-discharge fourier transform microwave spectra of ch3–cc–f,...

Chemical Physics Letters 375 (2003) 355–363

www.elsevier.com/locate/cplett

Molecular beam pulsed-discharge Fouriertransform microwave spectra of CH3–CBC–F,

CH3–(CBC)2–F, and CH3–(CBC)3–F

Susana Blanco, M. Eugenia Sanz, Santiago Mata, Alberto Lesarri,Juan C. L�oopez, Helmut Dreizler 1, Jos�ee L. Alonso *

Departamento de Qu�ıımica F�ıısica, Facultad de Ciencias, Universidad de Valladolid, E-47005 Valladolid, Spain

Received 1 May 2003; in final form 20 May 2003

Published online 14 June 2003

Abstract

The methylfluoroacetylenes CH3–(CBC)2–F and CH3–(CBC)3–F have been generated for the first time in a pulsed-

discharge nozzle and characterized by molecular beam Fourier transform microwave spectroscopy in the 5–26 GHz

frequency range. The spectroscopic constants B ¼ 1086:44824ð13Þ MHz, DJ ¼ 0:02044ð70Þ kHz, and DJK ¼ 7:083ð91ÞkHz of CH3–(CBC)2–F and B ¼ 478:908444ð34Þ MHz, DJ ¼ 0:003060ð98Þ kHz, and DJK ¼ 1:899ð22Þ kHz of CH3–

(CBC)3–F have been determined. In addition, the 13C isotopic species of CH3–CBC–F in their natural abundances have

been measured, and a partial substitution structure of CH3–CBC–F has been derived and compared with those of

related fluorine derivatives.

� 2003 Elsevier Science B.V. All rights reserved.

1. Introduction

Unsaturated fluorine-containing species have

been studied by different spectroscopic techniques

to determine their structures and to compare their

behaviour with that of related hydrocarbons or

other halogen-bearing molecules. These investiga-tions were limited because unsaturated fluorine-

* Corresponding author. Fax: +34-983-423204.

E-mail address: [email protected] (J.L. Alonso).1 Permanent address: Institut f€uur Physikalische Chemie der

Christian-Albrechts-Universit€aatKiel, Olshausenstr. 40, D-24098

Kiel, Germany.

0009-2614/03/$ - see front matter � 2003 Elsevier Science B.V. All r

doi:10.1016/S0009-2614(03)00863-7

containing compounds are not easy to synthesize

and because they are quite unstable in the normal

conditions of pressure and temperature. The dis-

covery of the efficient production of these com-

pounds in electric discharge experiments [1] boosted

their studies, and a number of fluorinated species

(H–(CBC)2–F [2,3], CH3–CBC–F [4], Cl–CBC–F[5], Br–CBC–F [5], I–CBC–F [6], F–CBC–CN[7–9], and F–(CBC)2–CN [10]) were characterized

by the analysis of their absorption spectra in the

millimeter-wave frequency region after their gen-

eration by dc glow discharges. Discharge methods

were later on combined with supersonic molecular

beams and Fourier transform techniques in the

ights reserved.

mail to: [email protected]

356 S. Blanco et al. / Chemical Physics Letters 375 (2003) 355–363

microwave spectral range [11–13], which lead to a

dramatic improvement in sensitivity.

We have recently constructed and implemented

a pulsed-discharge nozzle in our molecular beam

Fourier transform microwave spectrometer [14],

which has broadened the capabilities of this in-strument, routinely used for the production of

weakly bound complexes. Our first tests on the new

discharge system followed the work of Sutter and

Dreizler [15,16], and extended their investigation on

the rotational spectra of fluoroacetylenes with the

detection of rare isotopic species of fluorodiacety-

lene in their natural abundances and the identifi-

cation of the longer chains fluorotriacetylene andfluorotetracetylene [17,18].

As an extension of the studies on fluorine-

containing molecules we have investigated the

rotational spectra of the fluoromethylacetylenes

CH3–(CBC)n–F. Only the millimeter-wave spec-

trum of the normal species of CH3–CBC–F, thefirst member of the series, had been previously

detected after its production in a free-space cell bydc glow discharge [4]. The highest sensitivity of

pulsed-discharge molecular beam Fourier trans-

form microwave spectroscopy allowed us to detect

the next two members of this family of com-

pounds, CH3–(CBC)2–F and CH3–(CBC)3–F,and the 13C isotopomers of CH3–CBC–F. Herewe report the results obtained from the analysis of

Fig. 1. Cross-section of the pulsed-discha

their spectra. A partial rs structure has been cal-

culated for CH3–CBC–F, and compared with

those available in the literature for related mole-

cules. Ab initio calculations have also been carried

out for the three fluoroacetylenes observed here to

estimate their structures and dipole moments.

2. Experimental

The rotational spectra of the fluoromethylacet-

ylenes CH3–(CBC)n–F were observed using the

molecular beam Fourier transform microwave

spectrometer described in [14], which now incor-porates the pulsed-discharge nozzle shown in Fig. 1

for the generation of unstable species. Our dis-

charge nozzle is similar to those used by other re-

search groups [11–13]; it consists of two copper

electrodes and several Teflon spacers located in a

Teflon housing attached to the body of an electro-

mechanical valve. The dimensions of the discharge

nozzle have been changed from that reported on[17] to optimize the production of fluoromethyl-

acetylenes. Different inner diameters and thick-

nesses for the electrodes and the Teflon spacers have

been tried, as well as several nozzle diameters. The

new configuration uses a nozzle of 1 mm diameter

orifice and a much shorter Teflon spacer down-

stream the second electrode (closest to the mirror).

rge nozzle used in our experiment.

S. Blanco et al. / Chemical Physics Letters 375 (2003) 355–363 357

Operation conditions have been improved with

the addition of a small chamber connected to the

Fabry–P�eerot resonator by a guillotine valve. Ow-

ing to depositions in the nozzle of the species

generated in the electric discharge, it is necessary

to stop the experiment from time to time and cleanthe discharge nozzle. A linear motion feedthrough

allows to extract the nozzle while the vacuum in

the main chamber is maintained, which signifi-

cantly increases the operation efficiency. Generally

the experiment runs during a whole day without

servicing.

The species of interest are generated by applica-

tion of dc electric discharges to the appropriategaseous mixtures in the throat of the nozzle. Several

precursor gases have been employed: 2,3,4,5,

6-pentafluorotoluene (C6H3F5), binary (1:1) mix-

tures of (a) acetylene (HCBCH) and 3,3,3-trifluoro-propyne (CF3–CBCH), (b) vinilydene fluoride

(F2C@CH2) and propyne (CH3–CBCH), (c) pro-pyne and 3,3,3-trifluoropropyne, (d) 2,3,4,5,6-pen-

tafluorotoluene and diacetylene (HCBC–CBCH),and (e) trifluoromethane (CF3H) and propyne, and

ternarymixtures of (a) vinilydene fluoride, propyne,

and acetylene (1:1:1) and (b) vinilydene fluoride,

propyne, and diacetylene (1:1:1.5). The precursors

were typically seeded in Ne in concentrations of

approximately 0.5% each at backing pressures of

2 bar. The strongest signals for 1-fluoropropyne

were obtained with mixtures of �0.5% vinilydenefluoride and �0.5% propyne, �0.5% 3,3,3-trif-

luoropropyne and �0.5% propyne, and �0.5%trifluoromethane and �0.5% propyne in Ne. Al-

though signals of comparable intensity for CH3–

CBC–F were observed with these three mixtures,

the two latter ones yielded a less intense rotational

spectrum of CH3–(CBC)2–F, by factors of roughly1.3 and 4, respectively. Therefore, CH3–(CBC)3–Fwas searched for using a sample with vinilydene

fluoride and propyne as precursor gases.

Optimal signal to noise ratio of fluoroacetylenes

was achieved with molecular pulses of 0.50–0.65

ms together with microwave pulses of 0.3 ls at arepetition rate of 5 Hz. The electric discharge was

generally applied 0.20–0.25 ms after the beginning

of the molecular pulse, and maintained for ap-proximately 0.60 ms, until the microwave radia-

tion was introduced into the cavity. Several tests

have been performed applying output voltages of

different polarities to either the upstream or the

downstream electrode and grounding the other

one. Unlike what observed for H–(CBC)n–F[17,18], a more efficient production of CH3–

(CBC)n–F occurs when a negative voltage is ap-plied to the electrode upstream and the electrode

downstream is grounded. The more intense signals

were obtained with discharge voltages between

)2000 and )2600 V, the higher voltages needed to

optimize the production of the longest fluoro-

acetylenes. Frequencies were determined after

Fourier transformation of the 4k data point signal

in the time domain, recorded with 40 ns sampleinterval. Because the molecular beam enters the

Fabry–P�eerot resonator parallel to the microwave

radiation, each transition appears as a doublet

owing to the Doppler effect.

3. Results and discussion

3.1. CH3–CBC–F

1-Fluoropropyne was first detected by Oka-

bayashi et al. [4] in a dc glow discharge, and its

spectroscopic constants determined from the

analysis of its millimeter-wave spectrum in the

207–262 GHz frequency range. No information on

the rare isotopic species was obtained.The three lowest-J rotational transitions of

1-fluropropyne lie in the spectral region between

5 and 26 GHz and were readily observed with the

several precursor gases employed (see Table 1).

The J ¼ 2 ! 1 and 3! 2 rotational transitions

appeared as doublets, which correspond to the

closely spaced K ¼ 0 and K ¼ 1 components.

Transitions involving higher K levels are not ob-served because these levels are not sufficiently

populated in our jet-cooled experiment. The clas-

sical expression of a non-rigid symmetric top

Hamiltonian [19] was fitted to all measured tran-

sitions of 1-fluoropropyne using Pickett�s programSPFITPFIT [20]. Uncertainties of 20 and 2 kHz were

assigned to the millimeter-wave and microwave

transitions, respectively. The slightly improvedspectroscopic constants determined from this fit

are shown in Table 2.

Table 1

Rotational transitions (MHz) of CH3–CBC–F measured in this work

J 0 K 0 J 00 K 00 Obs. o:� c:a

1 0 0 0 6902.929 )0.0022 0 1 0 13 805.853 )0.0022 1 1 1 13 805.681 )0.0013 0 2 0 20 708.764 0.003

3 1 2 1 20 708.507 0.003

aObserved minus calculated from the spectroscopic constants of Table 2, resulting from the global fit of these transitions with those

previously measured [4].

Table 2

Spectroscopic constants (MHz) of CH3–(CBC)n–F, n ¼ 1–3

CH3–CBC–F CH3–(CBC)2–F CH3–(CBC)3–F

B 3451.46641(15)a 1086.44824(13) 478.908444(34)

DJ � 103 3.40944(69) 0.02044(70) 0.003060(98)

DJK � 103 43.1033(92) 7.083(91) 1.899(22)

HJK � 106 0.1092(35) – –

HKJ � 106 0.965(72) – –

rb 16.6 2.9 0.9

a Standard errors in parentheses in units of the last digit. Constants from the global fit of the rotational transitions of Table 1 with

those previously measured [4].bRms deviation of the fit in kHz.


Estimation of the spectroscopic constants forthe 13C species of CH3–CBC–F was aided by

ab initio calculations done at the B3LYP/

6-311+G(d,p) level of theory using the GAUSSIANAUSSIAN

98 package of programs [21]. The theoretical ro-

tational constants for the parent species were

compared to the experimental ones, and their ratio

used to scale accordingly the rotational constants

of the 13C isotopic species predicted with the abinitio structure. The microwave transitions ob-

served for each singly isotopically substituted 13C

isotopomers (see Table 3) in their natural abun-

dances (�1%) laid extremely close (within less than

Table 3

Measured rotational transitions (MHz) of the 13C isotopic species of

J 0 K 0 J 00 K 00 13CH3–CBC–F

Obs. o:� c:a

2 0 1 0 13 399.383 )0.0052 1 1 1 13 399.220 )0.0023 0 2 0 20 099.064 0.003

3 1 2 1 20 098.814 0.001

aObserved minus calculated from the spectroscopic constants of T

1 MHz) to their predicted frequencies and showedsimilar K splitting to that of the parent species (see

Fig. 2). Fits of these transitions using the same

Hamiltonian as for the normal isotopic species

yielded the B and DJK spectroscopic constants for

each 13C isotopomer given in Table 4.

From the rotational constants determined, a

partial rs structure has been derived for CH3–

CBC–F applying Kraitchman equations [22]:r(C1–C2)¼ 1.200(5) and r(C2–C3)¼ 1.459(3) �AA,where C1 refers to the atom bound to the F atom,

C2 is the central carbon, and C3 is the methylic

carbon (see Fig. 3). The uncertainties quoted have

CH3–CBC–F

CH3–13CBC–F CH3–CB13C–F

Obs. o:� c:a Obs. o:� c:a

13 765.136 0.001 13 779.104 0.002

13 764.965 )0.001 13 778.930 )0.00120 647.681 )0.001 20 668.632 )0.00120 647.428 0.001 20 668.376 0.000

able 4.

Fig. 2. Measured rotational transition J ¼ 2 ! 1 of CH3–13CBC–F, showing the distinctive K structure of a symmetric

top in our molecular beam. The amplitude Fourier transform

microwave spectrum was obtained after 600 accumulating

cycles.

Fig. 3. Derived rs structure of CH3–CBC–F (bond lengths in�AA and angles in �). Parameters in square brackets have been

assumed.


been calculated applying Costain�s formula [23]:

Dz ¼ K=jzj, with K ¼ 0:0015 �AA. The bond length

r(C1–F)¼ 1.282(4) �AA has been calculated from the

first moment condition along the a principal iner-tial axis (

Pi miai ¼ 0) assuming C3v symmetry for

the methyl group, with bond lengths r(C1–

H)¼ 1.090 �AA and angles \CCH ¼ 110:6�. The

quoted uncertainty in the C1–F bond distance is

believed to include the error due to the assumed

positions for the methylic hydrogens: changing

\CCH by 0.5� and r(C1–H) by 0.005 �AA results

in a change of 0.001 �AA in r(C1–F).The molecular rs structure derived for CH3–

CBC–F is compared in Table 5 with those of

related molecules. The rs parameters of the com-

parison molecules have been calculated where

necessary applying Kraitchman�s equations [22].

Uncertainties given have been calculated using

Costain�s formula [23]. The bond length CBC

Table 4

Spectroscopic constants (MHz) of the 13C isotopic species of CH3–C

13CH3–CBC–F CH3

B 3349.84963(41)a 3441

DJ � 103 [3.40944]b [3.40

DJK � 103 41.33(59) 42.3

rc 3.0 0.9

a Standard errors in parentheses in units of the last digit.b Parameters in square brackets were kept fixed to the values of pacRms deviation of the fit in kHz.

varies very slightly among the acetylenes listed in

Table 5, lying in the range 1.203 0.003 �AA, exceptfor CH3–CBC–F with a much shorter rs value forthis distance. The small accuracy of the CBCdistance of CH3–CBC–Cl arises from the error in

the coordinate of the C atom bound to the Cl

nucleus, that lies extremely close to the center of

mass. The C–C bond distance is practically in-variant among those acetylenes with a terminal

methyl group. For the fluoroacetylenes with a

terminal CF3 the C–C bond is significantly short-

ened, specially in the case of CH3–CBC–H. Ourderived rs value for the C–F bond length (1.282(4)�AA) is very similar to that determined for the relatedfluoroacetylene H–(CBC)2–F (1.2854(7) �AA [24]).

3.2. CH3–(CBC)2–F and CH3–(CBC)3–F

Preliminary rotational constants of CH3–

(CBC)2–F and CH3–(CBC)3–F have been calcu-

lated using two different approaches:

(i) By adding either one or two –CBC– frag-

ments to the rs structure of CH3–CBC–F (see Sec-

tion 3.1) using typical bond lengths. This yieldedthe values B ¼ 1085:56 MHz for CH3–(CBC)2–Fand B ¼ 477:80 MHz for CH3–(CBC)3–F.

BC–F

–13CBC–F CH3–CB13C–F

.28643(12) 3444.77831(16)

944] [3.40944]

3(17) 42.90(23)

1.2

rent 1-fluoropropyne.

Fig. 5. Rotational spectrum of the J ¼ 12 ! 11 transition of

CH3–(CBC)3–F, taken after 2540 accumulating cycles.

Fig. 4. Rotational spectrum of the J ¼ 5 ! 4 transition of

CH3–(CBC)2–F, taken after 30 accumulating cycles.

Table 5

Structural rs bond lengths (�AA) of CH3–CBC–F and several

related molecules

r(C1BC2) r(C2–C3)

CH3–CBC–Ha 1.2066 1.4586

CH3–CBC–Fb 1.200(5) 1.459(3)

CH3–CBC–Clc 1.20(6) 1.4585(18)

CF3–CBC–Hd 1.2017(19) 1.438(7)

CF3–CBC–Fe 1.193(3) 1.450(4)

aM. Le Guennec, J. Demaison, G. Wlodarczak, C. J.

Marsden, J. Mol. Spectrosc. 160 (1993) 471.b This work.c Calculated from the rotational constants of A.P. Cox, M.C.

Ellis, T. Perrett, J. Chem. Soc. Farad. Trans. 88 (1992) 2611.d Calculated from the rotational constants of A.P. Cox, M.C.

Ellis, A. C. Legon, A. Wallwork, J. Chem. Soc. Farad. Trans.

89 (1993) 2937.e Calculated from the rotational constants of A.P. Cox, M.C.

Ellis, T. D. Summers, J. Sheridan, J. Chem. Soc. Farad. Trans.

88 (199) 1079.


(ii) From ab initio calculations. The MP2 andB3LYP methods with the 6-31+G(d,p) and

6-311+G(d,p) basis sets were first employed to

calculate the rotational constant of CH3–CBC–F.As occurred for the fluoropolyacetylenes F–

(CBC)n–H [14], the B3LYP/6-311+G(d,p) method

provided the best agreement between the theoret-

ical and the experimental B value of CH3–CBC–F.This method was thus used to calculate the rota-tional constants of CH3–(CBC)2–F and CH3–

(CBC)3–F. The predicted values were corrected

according to the difference between the calculated

and experimental B of CH3–CBC–F, to obtain

B ¼ 1087:55 and 479.10 MHz for CH3–(CBC)2–Fand CH3–(CBC)3–F, respectively.

Transitions from CH3–(CBC)2–F, with the ex-

pected K splitting, were found very close to thepredicted frequencies, and observed with a signal

to noise ratio of 20 after a few seconds of inte-

gration time (see Fig. 4), a decrease of roughly 6

from that of CH3–CBC–F. Assuming that a sim-

ilar decrease in signal to noise ratio will occur in

going from CH3–(CBC)2–F to CH3–(CBC)3–F,transitions of CH3–(CBC)3–F were expected to be

quite weak. Therefore, it was searched for with ahigher number of accumulating cycles and using as

precursors vinilydene fluoride and propyne, which

yielded the strongest signals for CH3–(CBC)2–F.

With these conditions lines showing the distinctive

K structure of a symmetric top were detected with

a signal to noise ratio of about 7 after 2500 accu-

mulating cycles (see Fig. 5) and assigned to CH3–

(CBC)3–F.A total of eight aR-branch microwave transi-

tions ranging from J ¼ 4 to 11 of CH3–(CBC)2–Fand seven rotational transitions from J¼ 8 to 15 of

CH3–(CBC)3–F were measured in the K ¼ 0 and 1

ladders (see Tables 6 and 7). They were analyzed

using the standard symmetric top Hamiltonian [19]

to derive the spectroscopic constants of Table 2.

There is no doubt about the assignments of theobserved transitions to the two new fluoroacetyl-

enes: the rotational transitions disappear in the

absence of the electric discharge, indicating that

they arise from molecules produced in the

Table 6

Measured rotational transitions (MHz) of CH3–(CBC)2–F

J 0 K 0 J 00 K 00 Obs. o:� c:a

4 0 3 0 8691.580 )0.0014 1 3 1 8691.526 0.002

5 0 4 0 10 864.475 0.003

5 1 4 1 10 864.401 0.000

6 0 5 0 13 037.361 0.000

6 1 5 1 13 037.278 0.002

7 0 6 0 15 210.242 )0.0057 1 6 1 15 210.152 0.004

8 0 7 0 17 383.124 )0.0068 1 7 1 17 383.019 0.002

9 0 8 0 19 556.011 0.002

9 1 8 1 19 555.879 )0.00210 0 9 0 21 728.885 0.001

10 1 9 1 21 728.739 )0.00211 0 10 0 23 901.756 0.003

11 1 10 1 23 901.595 )0.002aObserved minus calculated from the spectroscopic constants of Table 2.

Table 7

Measured rotational transitions (MHz) of CH3–(CBC)3–F

J 0 K 0 J 00 K 00 Obs. o:� c:a

8 0 7 0 7662.529 0.000

8 1 7 1 7662.498 0.000

9 0 8 0 8620.342 )0.0029 1 8 1 8620.309 0.000

10 0 9 0 9578.155 )0.00210 1 9 1 9578.120 0.001

11 0 10 0 10 535.971 0.001

11 1 10 1 10 535.929 0.001

12 0 11 0 11 493.784 0.002

12 1 11 1 11 493.735 )0.00114 0 13 0 13 409.403 0.000

14 1 13 1 13 409.350 0.000

15 0 14 0 14 367.212 0.000

15 1 14 1 14 367.155 0.000

aObserved minus calculated from the spectroscopic constants of Table 2.


discharge; the lines are absent from the spectrum

when the F-containing precursor is removed from

the gas mixture, indicating that they correspond to

F-bearing molecules; the measured transitions

present the characteristic K splitting of symmetrictops, and no lines have been observed at subhar-

monic frequencies, which rules out the possibility

that we are observing heavier molecules than those

assigned; and finally, the spectroscopic constants

determined from the measured transitions are in

excellent agreement with those calculated ab initio

and those predicted from the derived rs structureof CH3–CBC–F.

The estimated decrement in signal to noise

ratio, after normalization with the number of ac-

cumulating cycles, from CH3–(CBC)2–F to CH3–(CBC)3–F is approximately 24. This decrease is

very similar to that of 26 observed in going from

H–(CBC)2–F to H–(CBC)3–F [17], and notably

larger than the factor of 6 decrease estimated

from CH3–CBC–F to CH3–(CBC)2–F. The dec-

rement cannot be attributed to a change in dipole


moment, since B3LYP/6-311+G(d,p) calculations

predict a dipole moment increase from 1.6 D for

CH3–CBC–F to 1.8 D for CH3–(CBC)2–F and

2.1 D for CH3–(CBC)3–F. The steep decrement in

the signal to noise ratio is most likely due to a less

abundant production of CH3–(CBC)3–F in ourmolecular beam with respect to the shorter flu-

oroacetylenes. Observation of the next member of

the series, CH3–(CBC)4–F, will not be possible

with the present conditions if a similar decrease in

signal intensity takes place.

Methylpolyynes CH3–(CBC)n–H (n ¼ 1,2) [25–

27] and methylcyanoacetylenes CH3–CBC–CN[28] and possibly CH3–(CBC)2–CN [29], moleculessimilar to those studied here, have been detected

towards several astronomical sources. Hydrogen

fluoride has been observed in various astronomic

environments [30–32] and AlF has been detected in

the inner shell of the evolved C-rich star

IRC+10216 [33,34]. The abundance of fluorine in

the interstellar medium is quite small in compari-

son with elements such as C or N, and recentchemical models indicate that F is almost com-

pletely in the form of HF in the interstellar me-

dium [35]. However, the observations of AlF and

HF in red giant stars imply a fluorine concentra-

tion in the inner circumstellar envelopes signifi-

cantly higher than that of the solar system. Other

fluorine-containing species might be present there

even if with extremely small abundances. Our dataon fluoromethylacetylenes could be useful for fu-

ture astronomical searches.

Acknowledgements

This work has been supported by Direcci�oonGeneral de Investigaci�oon (Ministerio de Ciencia yTecnolog�ııa), Grant BQU2000-0869 and Junta de

Castilla y Le�oon, Grant VA087/03. M.E.S. grate-

fully acknowledges the Ministerio de Ciencia y

Tecnolog�ııa for a Ram�oon y Cajal contract.

References

[1] G. Bieri, J.-P. Stadelmann, F. Thommen, J. Vogt, Helv.

Chim. Acta 61 (1978) 357.

[2] Y. Okabayashi, K. Tanaka, T. Tanaka, J. Mol. Spectrosc.

137 (1989) 9.

[3] Y. Okabayashi, N. Yamashita, Y. Sakai, M. Tanimoto,

J. Mol. Spectrosc. 193 (1999) 273.

[4] T. Okabayashi, M. Tanimoto, T. Ogata, J. Mol. Spectrosc.

168 (1994) 579.

[5] T. Okabayashi, M. Tanimoto, J. Mol. Spectrosc. 154

(1992) 201.

[6] T. Hirao, T. Okabayashi, M. Tanimoto, J. Mol. Spectrosc.

162 (1993) 358.

[7] K. Tanaka, T. Okabayashi, T. Tanaka, J. Mol. Spectrosc.

132 (1988) 467.

[8] T. Okabayashi, M. Tanimoto, K. Tanaka, J. Mol. Spec-

trosc. 174 (1995) 595.

[9] T. Okabayashi, K. Tanaka, T. Tanaka, J. Mol. Spectrosc.

195 (1999) 22.

[10] T. Okabayashi, M. Tanimoto, K. Tanaka, E. Hirota,

Chem. Phys. Lett. 230 (1994) 530.

[11] J.-U. Grabow, N. Heineking, W. Stahl, Z. Naturforsch.

46a (1991) 914.

[12] Y. Endo, H. Koguchi, Y. Ohshima, Faraday Discuss. 97

(1994) 341.

[13] M.C. McCarthy, W. Chen, M.J. Travers, P. Thaddeus,

Astrophys. J. Supp. Ser. 129 (2000) 611.

[14] J.L. Alonso, F.J. Lorenzo, J.L. L�oopez, A. Lesarri, S. Mata,

H. Dreizler, Chem. Phys. 218 (1997) 267.

[15] D.H. Sutter, H. Dreizler, Z. Naturforsch. 55a (2000)

695.

[16] D.H. Sutter, H. Dreizler, Z. Naturforsch. 56a (2001)

425.

[17] H. Dreizler, S. Mata, A. Lesarri, J.C. L�oopez, S. Blanco,

J.L. Alonso, Z. Naturforsch. 57a (2002) 76.

[18] J.L. Alonso et al., to be published.

[19] W. Gordy, R.L. Cook, Microwave Molecular Spectra,

Wiley, New York, 1984 (Chapter VI, Eq. (6.16)).

[20] H.M. Pickett, J. Mol. Spectrosc. 148 (1991) 371.

[21] M.J. Frisch et al., GAUSSIANAUSSIAN 98, Revision A.11, Gaussian,

Pittsburgh, PA, 2001.

[22] J. Kraitchman, Am. J. Phys. 21 (1953) 17.

[23] B.P. van Eijck, J. Mol. Spectrosc. 91 (1982) 348.

[24] L. Dore, L. Cludi, A. Mazzavillani, G. Cazzoli, C.

Puzzarini, Phys. Chem. Chem. Phys. 1 (1999) 2275.

[25] W.M. Irvine, B. H€ooglund, P. Friberg, J. Askne, J. Elld�eer,Astrophys. J. Lett. 248 (1981) L113.

[26] C.M. Walmsley, P.R. Jewell, L.E. Snyder, G. Winnewisser,

Astron. Astrophys. Lett. 134 (1984) L11.

[27] J.M. MacLeod, L.W. Avery, N.W. Broten, Astrophys. J.

Lett. 282 (1984) L89.

[28] N.W. Broten, J.M. MacLeod, L.W. Avery, W.M. Irvine, B.

H€ooglund, P. Friberg, �AA. Hjalmrson, Astrophys. J. Lett. 276

(1984) L25.

[29] L.E. Snyder, T.L. Wilson, C. Henkel, P.R. Jewel, C.M.

Walmsley, Bull. Am. Astron. Soc. 16 (1984) 959.

[30] L. Wallace, W. Livingston, J. Geophys. Res. 96 (1991)

15513.

[31] A. Jorissen, V.V. Smith, D.L. Lambert, Astron. Astrophys.

261 (1992) 164.


[32] D.A. Neufeld, J. Zmuidzinas, P. Schilke, T.G. Phillips,

Astrophys. J. 488 (1997) L141.

[33] J. Cernicharo, M. Gu�eelin, Astron. Astrophys. Lett. 183(1987) L10.

[34] L.M. Ziurys, A.J. Apponi, T.G. Phillips, Astrophys. J. 433

(1994) 729.

[35] C. Zhu, R. Krems, A. Dalgarno, N. Balakrishnan, Astro-

phys. J. 577 (2002) 795.

molecular beam pulsed-discharge fourier transform microwave spectra of ch3–cc–f,...

Documents