7 research outputs found

### Rotational Spectroscopy of 1â€‘Cyano-2-methylenecyclopropane (C<sub>5</sub>H<sub>5</sub>N)A Newly Synthesized Pyridine Isomer

The
gas-phase rotational spectrum of 1-cyano-2-methylenecyclopropane
(C1, C5H5N), an
isomer of pyridine, is presented for the first time, covering the
range from 235 to 500 GHz. Over 3600 a-, b-, and c-type transitions for the ground
vibrational state have been assigned, measured, and least-squares
fit to partial-octic A- and S-reduced distorted-rotor Hamiltonians
with low statistical uncertainty (Ïƒfit = 42 kHz).
Transitions for the two lowest-energy fundamental states (Î½27 and Î½26) and the lowest-energy overtone
(2Î½27) have been similarly measured, assigned, and
least-squares fit to single-state Hamiltonians. Computed vibrationâ€“rotation
interaction constants (B0â€“Bv) using the B3LYP and MP2
levels of theory are compared with the corresponding experimental
values. Based upon our preliminary analysis, the next few vibrationally
excited states form one or more complex polyads of interacting states via Coriolis and anharmonic coupling. The spectroscopic
constants and transition frequencies presented here form the foundation
for both future laboratory spectroscopy and astronomical searches
for 1-cyano-2-methylenecyclopropane

### Rotational Spectroscopy of 1â€‘Cyano-2-methylenecyclopropane (C<sub>5</sub>H<sub>5</sub>N)A Newly Synthesized Pyridine Isomer

The
gas-phase rotational spectrum of 1-cyano-2-methylenecyclopropane
(C1, C5H5N), an
isomer of pyridine, is presented for the first time, covering the
range from 235 to 500 GHz. Over 3600 a-, b-, and c-type transitions for the ground
vibrational state have been assigned, measured, and least-squares
fit to partial-octic A- and S-reduced distorted-rotor Hamiltonians
with low statistical uncertainty (Ïƒfit = 42 kHz).
Transitions for the two lowest-energy fundamental states (Î½27 and Î½26) and the lowest-energy overtone
(2Î½27) have been similarly measured, assigned, and
least-squares fit to single-state Hamiltonians. Computed vibrationâ€“rotation
interaction constants (B0â€“Bv) using the B3LYP and MP2
levels of theory are compared with the corresponding experimental
values. Based upon our preliminary analysis, the next few vibrationally
excited states form one or more complex polyads of interacting states via Coriolis and anharmonic coupling. The spectroscopic
constants and transition frequencies presented here form the foundation
for both future laboratory spectroscopy and astronomical searches
for 1-cyano-2-methylenecyclopropane

### Photoisomerization of (Cyanomethylene)cyclopropane (C<sub>5</sub>H<sub>5</sub>N) to 1â€‘Cyano-2-methylenecyclopropane in an Argon Matrix

Broad-band
ultraviolet photolysis (Î» > 200 nm) of (cyanomethylene)cyclopropane
(5) in an argon matrix at 20 K generates 1-cyano-2-methylenecyclopropane
(7), a previously unknown compound. This product was
initially identified by comparison of its infrared spectrum to that
predicted by an anharmonic MP2/6-311+G(2d,p) calculation. This assignment
was unambiguously confirmed by the synthesis of 1-cyano-2-methylenecyclopropane
(7) and observation of its authentic infrared spectrum,
which proved identical to that of the observed photoproduct. We investigated
the singlet and triplet potential energy surfaces associated with
this isomerization process using density functional theory and multireference
calculations. The observed rearrangement of compound 5 to compound 7 is computed to be endothermic (3.3 kcal/mol).
We were unable to observe the reverse reaction (7 â†’ 5) under the photochemical conditions

### Photoisomerization of (Cyanomethylene)cyclopropane (C<sub>5</sub>H<sub>5</sub>N) to 1â€‘Cyano-2-methylenecyclopropane in an Argon Matrix

Broad-band
ultraviolet photolysis (Î» > 200 nm) of (cyanomethylene)cyclopropane
(5) in an argon matrix at 20 K generates 1-cyano-2-methylenecyclopropane
(7), a previously unknown compound. This product was
initially identified by comparison of its infrared spectrum to that
predicted by an anharmonic MP2/6-311+G(2d,p) calculation. This assignment
was unambiguously confirmed by the synthesis of 1-cyano-2-methylenecyclopropane
(7) and observation of its authentic infrared spectrum,
which proved identical to that of the observed photoproduct. We investigated
the singlet and triplet potential energy surfaces associated with
this isomerization process using density functional theory and multireference
calculations. The observed rearrangement of compound 5 to compound 7 is computed to be endothermic (3.3 kcal/mol).
We were unable to observe the reverse reaction (7 â†’ 5) under the photochemical conditions

### Millimeter-Wave Spectroscopy, Xâ€‘ray Crystal Structure, and Quantum Chemical Studies of Diketene: Resolving Ambiguities Concerning the Structure of the Ketene Dimer

The pure rotational spectrum of diketene
has been studied in the
millimeter-wave region from âˆ¼240 to 360 GHz. For the ground
vibrational state and five vibrationally excited satellites (Î½<sub>24</sub>, 2Î½<sub>24</sub>, 3Î½<sub>24</sub>, 4Î½<sub>24</sub>, and Î½<sub>16</sub>), the observed spectrum allowed
for the measurement, assignment, and least-squares fitting a total
of more than 10â€¯000 distinct rotational transitions. In each
case, the transitions were fit to single-state, complete or near-complete
sextic centrifugally distorted rotor models to near experimental error
limits using Kisielâ€™s ASFIT. Additionally, we obtained less
satisfactory least-squares fits to single-state centrifugally distorted
rotor models for three additional vibrational states: Î½<sub>24</sub> + Î½<sub>16</sub>, Î½<sub>23</sub>, and 5Î½<sub>24</sub>. The structure of diketene was optimized at the CCSDÂ(T)/ANO1
level, and the vibrationâ€“rotation interaction (Î±<sub><i>i</i></sub>) values for each normal mode were determined
with a CCSDÂ(T)/ANO1 VPT2 anharmonic frequency calculation. These Î±<sub><i>i</i></sub> values were helpful in identifying the previously
unreported Î½<sub>16</sub> and Î½<sub>23</sub> fundamental
states. We obtained a single-crystal X-ray structure of diketene at
âˆ’173 Â°C. The bond distances are increased in precision
by more than an order of magnitude compared to those in the 1958 X-ray
crystal structure. The improved accuracy of the crystal structure
geometry resolves the discrepancy between previous computational and
experimental structures. The rotational transition frequencies provided
herein should be useful for a millimeter-wave or terahertz search
for diketene in the interstellar medium

### Millimeter-Wave Spectroscopy, Xâ€‘ray Crystal Structure, and Quantum Chemical Studies of Diketene: Resolving Ambiguities Concerning the Structure of the Ketene Dimer

The pure rotational spectrum of diketene
has been studied in the
millimeter-wave region from âˆ¼240 to 360 GHz. For the ground
vibrational state and five vibrationally excited satellites (Î½<sub>24</sub>, 2Î½<sub>24</sub>, 3Î½<sub>24</sub>, 4Î½<sub>24</sub>, and Î½<sub>16</sub>), the observed spectrum allowed
for the measurement, assignment, and least-squares fitting a total
of more than 10â€¯000 distinct rotational transitions. In each
case, the transitions were fit to single-state, complete or near-complete
sextic centrifugally distorted rotor models to near experimental error
limits using Kisielâ€™s ASFIT. Additionally, we obtained less
satisfactory least-squares fits to single-state centrifugally distorted
rotor models for three additional vibrational states: Î½<sub>24</sub> + Î½<sub>16</sub>, Î½<sub>23</sub>, and 5Î½<sub>24</sub>. The structure of diketene was optimized at the CCSDÂ(T)/ANO1
level, and the vibrationâ€“rotation interaction (Î±<sub><i>i</i></sub>) values for each normal mode were determined
with a CCSDÂ(T)/ANO1 VPT2 anharmonic frequency calculation. These Î±<sub><i>i</i></sub> values were helpful in identifying the previously
unreported Î½<sub>16</sub> and Î½<sub>23</sub> fundamental
states. We obtained a single-crystal X-ray structure of diketene at
âˆ’173 Â°C. The bond distances are increased in precision
by more than an order of magnitude compared to those in the 1958 X-ray
crystal structure. The improved accuracy of the crystal structure
geometry resolves the discrepancy between previous computational and
experimental structures. The rotational transition frequencies provided
herein should be useful for a millimeter-wave or terahertz search
for diketene in the interstellar medium

### Carbonyl Diazide, OC(N<sub>3</sub>)<sub>2</sub>: Synthesis, Purification, and IR Spectrum

Carbonyl diazide (<b>1</b>), OCÂ(N<sub>3</sub>)<sub>2</sub>, is prepared by reaction of triphosgene and tetra-<i>n</i>-butylammonium azide in a solution of diethyl ether or
dimethyl ether.
The advantage of this synthetic method, relative to other procedures,
is that the use of triphosgene, OCÂ(OCCl<sub>3</sub>)<sub>2</sub>,
mitigates the need to use highly poisonous reagents such as phosgene,
OCCl<sub>2</sub>, or chlorofluorocarbonyl, OCÂ(Cl)ÂF. The identity and
purity of OCÂ(N<sub>3</sub>)<sub>2</sub> are established by gas-phase
IR spectroscopy, which reveals the presence of both <i>synâ€“syn</i> and <i>antiâ€“syn</i> conformers. Computed anharmonic
vibrational frequencies and infrared intensities of carbonyl diazide
(<b>1</b>) display excellent agreement with experiment, and
reveal the presence of strong Fermi resonances