Reactions of laser-ablated tellurium atoms with oxygen molecules: Matrix isolation infrared and DFT studies

Article abstract of DOI:10.1016/j.molstruc.2007.06.021

Laser ablation of tellurium was carried out using the second harmonic Nd:YAG laser in the presence of oxygen molecules in argon/nitrogen matrices. The major species obtained in the Ar matrix were Te₂O₂, TeO₂, Te₂

Full text of DOI:10.1016/j.molstruc.2007.06.021

Available online at www.sciencedirect.com
Journal of Molecular Structure 876 (2008) 240–249
www.elsevier.com/locate/molstruc
Reactions of laser-ablated tellurium atoms with oxygen
molecules: Matrix isolation infrared and DFT studies
*
K. Sundararajan , K. Sankaran, V. Kavitha
Materials Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India
Received 16 April 2007; received in revised form 19 June 2007; accepted 21 June 2007
Available online 30 June 2007
Abstract
Laser ablation of tellurium was carried out using the second harmonic Nd:YAG laser in the presence of oxygen molecules in argon/
nitrogen matrices. The major species obtained in the Ar matrix were Te2O2, TeO2, Te2O4 and the minor species were TeO, Te2O and
TeO3. In N2 matrix, in addition to the above primary ablation products, reaction products TeN and Te2N were also observed. The struc-
ture, energies and the vibrational frequencies of different tellurium oxide and nitride species were carried out using DFT calculations. The
computed vibrational frequencies were corroborated with experimental frequencies.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Laser ablation; Tellurium; Matrix isolation; Infrared
1. Introduction
dicted TeO2 to have a bent structure with a bond angle
110 3° similar to that of SeO2. They have also assigned
features due to tellurium monoxide dimers (TeO)2, tellu-
rium dioxide dimers (TeO2)2 and trimers (TeO2)3 and pre-
dicted the structure of (TeO)2 dimer to be cyclic.
Spoliti et al. [4] used a similar technique as that of Mue-
now et al. and studied the spectrum of TeO2 isolated in
nitrogen matrix and assigned the features observed at
848.3, 831.7 and 294.0 cmꢀ1 to the t3, t1 and t2 modes of
TeO2, respectively. From the vibrational data they calcu-
lated the gas phase vibrational frequencies of TeO2 using
the empirical relation reported by Hastie et al. [5].
Konings et al. [6] studied the vibrational spectrum of the
TeO2 vapor in a high temperature gas cell at 1250 K. They
observed seven absorption bands which were assigned to
three fundamental modes and four overtone/combination
bands of gaseous TeO2. In another paper, Konings et al.
[7] computed the structure of TeO2 using coupled cluster
CCSD(T) and MP2 methods. From the calculations at
MP2 level, the vibrational frequencies of gaseous TeO2
were reassigned. Several groups have carried out ab initio
computations on tellurium dioxide and higher tellurium
oxide clusters [8–12].
Tellurium is one of the reactive fission products gener-
ated in the nuclear reactor. It is a highly volatile species
and to study its behavior is of great concern under normal
and in extreme conditions. Tellurium can form host of
compounds with fuel and cladding materials [1]. Under
off-normal conditions, tellurium might vaporize as tellu-
rium dimer (Te2) and as Te–O bearing species [2].
Muenow et al. [3] studied the vaporization, thermody-
namics and structures of species in tellurium–oxygen sys-
tem by Knudsen cell (K-cell) coupled with matrix
isolation (MI) infrared technique. Fundamental frequen-
cies obtained from the infrared absorptions for the different
tellurium oxide species trapped at low temperature in
argon and neon matrices were used for calculating the
thermodynamic functions at various temperatures. From
the mass spectrometric experiments, they concluded that
the most abundant species formed were TeO and TeO2 in
the temperature range 782–903 K. Furthermore, they pre-
*
Corresponding author.
E-mail address: sundar@igcar.gov.in (K. Sundararajan).
0022-2860/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.06.021

K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
241
As can be seen, only K-cell coupled with MI infrared
studies were carried out on TeO2 in argon, nitrogen and
neon matrices; and no laser ablation coupled with MI of
Te + O2 system was reported in the literature. We have
therefore in the present work undertaken laser ablation
of Te in the presence of O2 in Ar/N2 matrices and studied
the species formed using infrared spectroscopic method.
The objectives are: (1) to identify the reaction products of
the laser-ablated species of Te + O2 in Ar and N2 matrices,
(2) to compare the species produced in the laser ablation-
MI of Te + O2 with those of K-cell MI experiments on
TeO2, (3) to corroborate the experimental frequencies with
the calculated frequencies for various tellurium oxide and
nitride species and (4) to compare the various oxide and
nitride species formed in tellurium with those of selenium.
DFT/B3LYP method. The LanL2DZ basis sets built in
the Gaussian-98 program [15] were employed for the tel-
lurium atoms and aug-cc-PVDZ basis sets were employed
for the oxygen and nitrogen atoms. Calculations were
also performed using LanL2DZdp ECP polarization
functions for tellurium atoms taken from EMSL basis
set library [16]. Tables 1 and 2 give the structural param-
eters, vibrational frequencies and the zero-point corrected
(ZPE) energies for the various tellurium oxide and nitride
species using LanL2DZ basis sets for tellurium whereas
Tables 3 and 4 give the frequencies using LanL2DZdp
basis sets. Figs. 1 and 2 show the structures of different
tellurium oxide and nitride species obtained by DFT
method.
4. Results and discussion
2. Experimental
Initially, the infrared spectra of laser-ablated products
of Te + O2 reaction in argon and nitrogen matrices will
be presented and later the vibrational assignments for the
observed bands with DFT calculations using LanL2DZ
basis sets for the tellurium atoms and the reaction mecha-
nisms for the formation of various tellurium oxide species
will be discussed.
The technique of pulsed laser-ablation and matrix inves-
tigation used in these experiments was described elsewhere
[13,14]. High-purity argon/nitrogen (Iolar, Grade I, M/s
Bhoruka Gases Limited, India) and oxygen (Commercial
Grade, M/s Inox Air Products, India) were used as matrix
gases in these experiments.
The second harmonic (532 nm) of a pulsed Nd:YAG laser
(Continuum, Model NY61-10), operated in the Q-switched
mode, at a repetition rate of 10 Hz was used for ablation.
The laser pulse had a temporal width of 10 ns. Typically,
20–40 mJ pulses were focused onto the sample, using a
100 mm focal length Suprasil lens. The laser beam was inci-
dent on the sample at a near-45° angle. The irradiance of such
a focused beam was calculated to be 108 W/cm2, resulting in
temperatures >2500 K at the focal point on the sample.
Pure tellurium powder (M/s Leico Industries Inc., USA,
purity: 99.99%) dried under IR lamp and used for making
the pellet. The pellet was sintered for 5 h under argon flow
at 250 °C. The pellet was kept at a distance of 60 mm from
the cold tip. The position of the laser beam on the sample
was varied manually to expose a fresh surface to the laser
beam continuously. This arrangement ensured efficient
ablation during the entire course of the experiment.
The laser-ablated species from the sample were deposited
along with Ar/N2 at a rate of ꢁ3 mmol/h onto a 12 K KBr
window for 1–2 h. Infrared spectrum of the deposited spe-
cies was recorded using a BOMEM MB100 FTIR, operat-
ing at a resolution of 1 cmꢀ1. Photolysis was carried out
using a 150 W broad band Xe UV source (M/s Spectral
Energy Inc.) and annealing cycles at 25 K were also carried
out and an infrared spectrum was again recorded.
4.1. Te + O2/Ar system
Fig. 3a shows the infrared spectra of laser-ablated Te(s)
deposited using 10% O2 in argon matrix and the product
absorption bands are listed in Table 5. The major peaks
are observed at 1074.2, 1039.0, 841.4 and 617.7 cmꢀ1. In
addition, we also observed a number of peaks with moder-
ate to weak intensities at 886.2, 881.4, 865.0, 858.7, 823.5,
782.5, 591.6 and 538.6 cmꢀ1. The features due to ozone
(O3) in argon matrix were observed at 1039.0 and 702.5
(not shown) cmꢀ1 [17]. The spectral feature observed at
782.5 cmꢀ1 is due to TeO and the features observed at
841.4 and 823.5 cmꢀ1 are assigned to the t3 and t1 vibra-
tions of TeO2 in Ar matrix. These assignments were based
on the earlier K-cell coupled with matrix isolation infrared
experiments, where the vapor phase species over TeO2(s) at
a maximum temperature of 973 K were trapped in argon
and neon matrices [3,4]. We also observed the combination
bands 2t1 – t2 and t1 + t2 of TeO2 in argon matrix at
1328.3 and 1111.4 cmꢀ1 that agreed well with the earlier
reported values [7]. Fig. 3b shows the infrared spectrum
recorded after the matrix was annealed at 25 K for
15 min. As can be seen from the spectrum that there is
no substantial change in intensities of the peaks because
of annealing. Fig. 3c shows the spectrum after the matrix
was photolysed using a broadband UV source for 15 min.
On photolysis, features at 1074.2 and 782.5 cmꢀ1 vanished
completely whereas features at 886.2, 881.4, 841.4, 617.7,
591.6 and 538.6 cmꢀ1 gained in intensity. On further
annealing the matrix at 25 K for 15 min (Fig. 3d), all the
major peaks gained very less intensity when compared to
the photolysed spectra.
All our experiments were performed using 14N2 and
16O2. Due to non-availability of 15N2 and 18O2 we could
not perform the isotopic experiments.
3. Computations
The geometries and vibrational frequencies of various
tellurium oxide and nitride species were calculated using

242
K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
Table 1
Frequency (cmꢀ1), intensity (km/mol), and structure calculations for diatomic, triatomic and tetraatomic tellurium–oxygen compounds using B3LYP
method
d
Energy (hartrees)e
˚
Molecule
Frequencies (intensity)
Bond lenghts (A)
Bond angle (°)
TeO (a)
787.5(14)
1.825
1.782
2.003
2.005, 1.275
2.022, 2.766
2.758, 1.810
1.954
–
ꢀ83.19820
ꢀ158.44797
ꢀ158.36191
ꢀ158.34826
ꢀ91.286699
ꢀ91.282526
ꢀ91.270955
ꢀ233.59075
OTeOa (b)
284.3(27), 850.0(10), 863.7(84)
492.5(3), 609.7(14), 906.4(21)
313.7(0), 547.3(17), 1203.1(384)
199.2(1), 482.0(1), 575.2 (34)
126.7(5), 198.1(11), 787.1(97)
141.6(1), 428.0(14), 662.8(71)
174.3(38), 260.6(30), 260.7(30), 810.4(0), 864.3(57),
864.5(57),
111.6
68.5
127.5
46.9
130.5
131.5
120.0
Cyclic-O2Tea (c)
TeOOa (d)
Cyclic-TeTeOb (e)
TeTeOb (f)
TeOTeb (g)
c
TeO3 (h)
1.775
cis-OOTeOc (i)
trans-OOTeOc (j)
OOOTec (k)
118.4(3), 262.9(5), 336.9(0), 525.0(20), 849.6(68),
1139.1(333)
144.2(14), 178.4(3), 294.4(5), 535.6(7), 844.8(87),
1096.4(361)
113.2(0), 165.0(0), 228.9(3), 488.1(8), 739.8(25),
1435.0(788),
129.4(1), 179.9(11), 238.4(16), 473.3(9), 585.8(36),
856.5(98)
187.7 (0), 258.5(0), 298.6(0), 363.5(128), 499.2(68),
701.6(0)
94.7(1), 100.7(0), 184.7(5), 445.6(19), 624.5(59),
838.8(132)
75.0(3), 138.7(0), 207.2(4), 257.2(2), 495.6(9),
1159.3(645)
75.6(12), 157.8(21), 191.6(0), 228.4(0), 284.3(0),
326.7(50),
1.295, 2.000, 1.783
1.308, 1.993, 1.786
1.220, 1.698, 1.888
120.2, 104.9, 0.0f
118.2, 103.5, 180.0f
112.7, 116.7
ꢀ233.56122
ꢀ233.55779
ꢀ233.50130
ꢀ166.50413
ꢀ166.49535
ꢀ166.48866
ꢀ166.41778
ꢀ316.97586
g
Exocycle Te2O2 (l)
2.070, 1.945, 1.779,
2.843
1.999
46.7, 111.3
Cyclic(TeO)2 (m)
106.5, 73.5, 0.0f
129.5, 103.4, 179.9f
101.4, 119.2, 180.0f
g
TeOTeOg (n)
TeTeOOg (o)
(TeO2)2 (p)
1.998, 1.914, 1.788
2.662, 2.061, 1.287
1.973, 1.769
100.7, 79.2, 103.9, 101.8f,
ꢀ101.8f
467.6(0), 534.9(90), 617.2(437), 632.1(0), 879.1(136),
880.3(0)
LanL2DZ basis set was used for tellurium and aug-cc-PVDZ for oxygen atom.
a
Relative energy of isomers 0, +54, +63 kcal/mol going down the column.
Relative energy of isomers 0, +3, +10 kcal/mol going down the column.
Relative energy of isomers 0, +19, +21, +56 kcal/mol going down the column.
Bond lengths given for molecule, left to right, respectively.
ZPE corrected energy.
b
c
d
e
f
Diheadral angle.
g
Relative energy of isomers 0, +6, +10, +54 kcal/mol going down the column.
4.2. Te + O2/N2 system
substantially but the features at 778.7, 1074.2 and
1575.2 cmꢀ1 vanished completely. On further annealing
(Fig. 4d) the matrix at 25 K for 15 min all the major
features gained very less intensities when compared to the
photolysed spectra.
Fig. 4a shows the infrared spectra of laser-ablated Te(s)
using 10% O2 in nitrogen matrix and the product absorp-
tion bands are listed in Table 6. Features due to common
species of nitrogen oxides such as NO, N2O, NO2 were
observed at 187ꢀ4.6, 2235.0, 1616.2 and the nitrogen radi-
4.3. Vibrational assignments for each tellurium oxide and
nitride species
cals N3 and N3 at 1657.6 and 2003.4 cmꢀ1, respectively,
ꢀ
which agree well with the reported values [18,19]. In N2
matrix, the strongest bands were observed at 1074.2,
1042.9 and 848.1 cmꢀ1 (Fig. 4a). The features due to ozone
(O3) in nitrogen matrix were observed at 1042.9 and
704.5 cmꢀ1 (not shown) [17]. We also observed features
with moderate intensities at 1575.2, 973.5, 790.3, 784.0
and 778.7 cmꢀ1 and with very weak features at 538.6,
588.2, 623.4, 619.6 and 881.4 cmꢀ1. The features observed
at 848.1 and 833.2 cmꢀ1 were due to t3 and t1 vibrations
of TeO2 in N2 matrix [4]. On annealing the matrix at
25 K (Fig. 4b) the changes in the intensities of all the fea-
tures were moderate. On photolysis (Fig. 4c), the intensity
of features at 881.4, 623.4/619.6 and 538.6 cmꢀ1 increased
4.3.1. TeO
The feature observed at 782.5 cmꢀ1(Ar) and 778.7 cmꢀ1(N2)
bands are assigned to the tellurium monoxide, which is in
good agreement with the previous reported values [3].
The DFT calculations using aug-cc-PVDZ basis sets pre-
dicted a value of 787.5 cmꢀ1, which corroborates well with
the observed value. The calculated bond length between Te
˚
and O atoms is 1.825 A and agrees well with the experimen-
tal value of 1.828 A [20]. Ab initio computation by Nogu-
era et al. [12] using B3LYP/3-21G** basis set on TeO
predicted the fundamental to occur at 795 cmꢀ1. Tellurium
monoxide may be produced by the reaction (1), which is
˚

K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
243
Table 2
Frequency (cmꢀ1), intensity (km/mol), and structure calculations for diatomic and triatomic tellurium–nitrogen compounds using B3LYP method
d
Energy (hartrees)e
˚
Molecule
Frequencies (intensity)
Bond lenghts (A)
Bond angle (°)
TeN (a)
757.5(14)
1.856,
1.911
–
ꢀ62.70963
ꢀ70.801000
ꢀ70.744593
ꢀ117.54872
ꢀ117.51248
ꢀ117.30861
ꢀ137.95553
ꢀ137.89474
TeNTea (b)
TeTeNa (c)
NNTeb (d)
N2Teb (e)
NTeNb (f)
TeNOc (g)
NTeOc (h)
152.1(3), 383.5(10), 860.9(268)
110.5(3), 161.0(13), 830.5(58)
356.8(2), 357.5(3), 389.6(10), 2195.4(432)
193.2(3), 288.6(5), 2105.4(176)
66.7(14), 816.4(0), 881.4(16)
349.4(1), 463.1(35), 1694.8(775)
205.8(18), 582.4(8), 789.7(30)
143.7
110.6
180.0
76.4
170.7
138.9
108.1
3.019, 1.825
1.126, 2.000
1.136, 2.432
1.813
2.008, 1.181
1.804, 1.939
LanL2DZ basis set was used for tellurium and aug-cc-PVDZ for oxygen and nitrogen atoms.
a
Relative energy of isomers 0, +35, +166 kcal/mol going down the column.
Relative energy of isomers 0, +23, +150 kcal/mol going down the column.
Relative energy of isomers 0, +38 kcal/mol going down the column.
Bond lengths given for molecule, left to right, respectively.
b
c
d
e
ZPE corrected energy.
Table 3
Table 4
Frequency (cmꢀ1), intensity (km/mol), calculations for diatomic, triatomic
and tetraatomic tellurium–oxygen compounds using B3LYP method
Frequency (cmꢀ1), intensity (km/mol), and energy calculations for
diatomic and triatomic tellurium–nitrogen compounds using B3LYP
method
Molecule
Frequencies (intensity)
Molecule
Frequencies (intensity)
TeO (a)
802.9(21)
OTeO (b)
Cyclic-O2Te (c)
TeOO (d)
CyclicTeTeO (e)
TeTeO (f)
TeOTe (g)
TeO3 (h)
277.5(28), 848.4(10), 867.5(93)
499.6(6), 616.5(14), 895.9(19)
312.3(0), 543.6(16), 1191.3(371)
212.9(1), 466.4(6), 585.5(36)
146.6(7), 225.3(12), 781.3(106)
136.8(1), 413.5(14), 673.7(62)
192.7(36), 264.0(30), 264.4(30), 810.3(0),
871.4(58),871.8 (58)
TeN (a)
767.9(11)
TeNTe (b)
TeTeN (c)
NNTe (d)
N2Te (e)
NTeN (f)
TeNO (g)
NTeO (h)
150.2(4), 377.6(11), 887.5(264)
126.8(6), 213.6(1), 567.2(16)
351.2(1), 351.6(1), 391.5(10), 2192.0(438)
194.6(3), 295.8(5), 2094.0(188)
66.7(14), 816.4(0), 881.4(16)
351.7(1), 461.1(34), 1689.5(787)
200.6(19), 602.6(8), 806.7(38)
cis-OOTeO (i)
trans-OOTeO (j)
OOOTe (k)
118.4(3), 265.5(5), 337.0(0), 516.7(21), 857.2(70),
1126.2(321)
137.1(12), 175.0(3), 286.8(5), 533.3(7), 852.4(92),
1085.7(349)
110.4(0), 155.5(1), 225.4(2), 497.3(6), 734.9(24),
1453.4(841)
138.9(2), 194.8(14), 227.7(15), 456.5(12),
587.6(40), 857.8(103)
185.2(0), 258.8(0), 296.6(29), 356.9(136),
500.9(66), 690.9(0)
84.8(1), 99.4(0), 178.3(5), 420.4(15), 636.8(58),
846.2(141)
LanL2DZdp basis set was used for tellurium and aug-cc-PVDZ for oxygen
and nitrogen atoms.
isomer OTeO, DFT calculations predicted the bond length
˚
between Te and O to be 1.782 A and the bond angle
Exocycle-Te2O2 (l)
Cyclic(TeO)2 (m)
TeOTeO (n)
\OTeO to be 111.6 ° clearly showing the molecule to have
a bent structure. Earlier calculations on TeO2 by Konings
et al. [7] and Noguera et al. [12] also predicted similar
results.
The 841.4, 823.5 cmꢀ1 (Ar) and 848.1, 833.2 cmꢀ1 (N2)
features were assigned to the t3 and t1 modes of TeO2,
respectively. These assignments agree well with the earlier
K-cell coupled with matrix isolation experiments [3,4].
The calculated frequencies for t3 = 863.7 cmꢀ1 and
t1 = 850.0 cmꢀ1 modes are higher than those observed in
argon matrix by 2.6%, 3.2% and in nitrogen matrix by
1.8%, 2.0%, respectively. The agreement is excellent consid-
ering the approximations involved in the DFT calculation.
The observed increase in TeO2 features in both the matrices
could probably be due to the insertion of tellurium atom
into the oxygen molecule under UV irradiation. TeO2 can
be formed by the following reaction (2)
TeTeOO (o)
76.2(4), 137.2(0), 227.2(5), 262.3(3), 496.6(7),
1122.3(628)
80.0(12), 153.1(20), 186.4(0), 221.4(0), 278.7(0),
320.2(48), 457.4(0) 533.2(86), 610.7(436), 615.1(0),
877.6(145), 879.7(0)
(TeO2)2 (p)
LanL2DZdp basis set was used for tellurium and aug-cc-PVDZ for oxygen
atom.
endothermic by +26.9 kcal/mol [21–23] and this excess
energy can be obtained from the laser-ablated plumes.
Te þ O2 ! TeO þ OðDE ¼ þ26 kcal=molÞ
ð1Þ
4.3.2. TeO2
Te þ O2 ! OTeOðDEðB3LYPÞ ¼ ꢀ30:0 kcal=molÞ
ð2Þ
Computations predicted three possible isomers for the
TeO2; OTeO, cyclic-TeOO and TeOO. Fig. 1b–d shows
the structure of these isomers and Table 1 gives the geomet-
rical parameters, vibrational frequencies and the ZPE cor-
rected energies for these isomers. For the lowest energy
The other two possible isomers for the TeO2 are cyclic-
OTeO and TeOO which are less stable by 54 and 63 kcal/
mol. Experimentally, we have not discerned any feature
corresponding to these isomers.

244
K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
Te
a
b
c
d
Te
O
Te
Te
O
O
O
O
O
O
O
e
h
f
g
O
O
Te
Te
Te
Te
Te
Te
Te
O
i
j
Te
O
O
O
O
Te
O
O
O
O
k
n
l
m
O
O
Te
O
Te
Te
O
O
O
O
O
Te
Te
o
p
Te
O
O
O
Te
Te
Te
O
Te
O
Te
O
O
Fig. 1. Structures of the different tellurium oxide species calculated at B3LYP/aug-cc-PVDZ method.
4.3.3. TeO3
865.0 cmꢀ1 in Ar matrix to TeO3 isomer. In the N2 matrix,
we could not observe the features due to TeO3 isomer, proba-
bly the isomer being unstable. A similar result was obtained
for the UO3 species when uranium oxide was laser ablated in
nitrogen matrices [13]. Experimentally, we have not discerned
any feature corresponding to the other TeO3 isomers.
DFT calculations predicted four possible isomers for TeO3;
planar-TeO3, cis-OTeOO, trans-OTeOO and OOOTe.
Fig. 1h–k shows the structure of the isomers and Table 1 gives
the structural parameters, frequencies and ZPE corrected
energies for all the isomers. DFT computations for the TeO3
(D3h) showed the bond angle between O–Te–O to be 120.0 °
˚
and the bond distance between Te and O to be 1.775 A, which
4.3.4. Te2O2
is a global minima on the potential energy surface. The other
three isomers are higher in energy and less stable by 19–
60 kcal/mol when compared to the planar-TeO3 isomer. The
calculated frequencies for the TeO3 isomer occur as a doubly
Calculations predicted the most stable Te2O2 isomer to
be an exocycle-Te2O2 similar to that of exocycle-Se2O2
[24] with a C1 symmetry; it has a three-membered TeTeO
ring and contains an exocyclic-Te@O unit (Fig. 1l). The
next higher energy isomer has a four-membered cyclic
structure, which is less stable by 6 kcal/mol. Muenow
et al. [3] assigned features observed near 520.0 and
650.0 cmꢀ1 to the cyclic (TeO)2 and predicted TeOTe bond
angle to be 100 °. Their assignments were based on the
results obtained for analogous cyclic-(SnO)2 [25]. DFT cal-
culations also predicted two other possible isomers, TeO-
TeO and TeTeOO which are less stable by 10 and
degenerate Te–O stretching mode at 864.3 and 864.5 cmꢀ1
.
Experimentally, we observed a doublet feature at 858.7 and
865.0 cmꢀ1 in Ar matrix and both these features increased in
intensity on photolysis and annealing cycle experiments as
well, clearly indicating that they belong to the same species.
As can be seen from the Table 6 that there is a very good agree-
ment between the calculated and experimental frequencies.
Hence, we assign the features observed at 858.7 and

K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
245
a
d
b
c
Te
f
N
Te
Te
N
Te
Te
N
Te
e
Te
N
N
Te
N
N
N
N
g
i
h
N
Te
O
Te
N
O
N
N
j
N
N
Te
Te
Te
Te
Fig. 2. Structures of the different tellurium nitride species calculated at B3LYP/aug-cc-PVDZ method.
50 kcal/mol, respectively. Fig. 1l–o shows the structures of
4.3.5. Te2O
different Te2O2 isomers.
DFT calculations have predicted the most stable isomer
of Te2O to be a cyclic-TeTeO. The cyclic-Te2O isomer has
a stretching fundamental at 575.2 cmꢀ1. We observed a
very weak feature at 591.6 cmꢀ1 (Ar) and 588.2 cmꢀ1
(N2). This feature gained in intensity on annealing cycle
and photolysis. The calculated value agrees well within
2.7% (Ar) and 2.2% (N2) when compared with the experi-
mental frequencies. Hence, we assign the feature observed
to the cyclic-Te2O isomer.
DFT calculations also predicted a bent TeTeO molecule
with a strong Te–O fundamental at 787.1 cmꢀ1, which is
very close to the TeO frequency at 787.5 cmꢀ1 and the
‘‘open’’ or ‘‘ozone-like’’ TeOTe isomer with a feature at
662.8 cmꢀ1. These two species are less stable by 2–
10 kcal/mol. We did not discern any vibrational features
due to these species. Fig. 1e–g shows the structures and
Table 1 gives the ZPE corrected energies of all the three
isomers.
In our laser-ablation experiment of Te(s) in 10% O2/Ar or
N2 we observed a very strong feature at 1074.2 (Ar) and
1073.7 (N2) cmꢀ1 in the as-deposited spectra. On photolysis
this feature vanished completely in both the matrices, clearly
showing that the feature is unstable on UV irradiation. Barb-
son et al. [24] studied the species formed when selenium was
discharged/heated in the presence of O2 in argon matrix. They
observed a new feature at 1404.5 cmꢀ1 and have assigned it to
(Se2)(O2). On vacuum-UV photolysis, the intensity of this fea-
ture decreased and a new feature was observed at 1061 cmꢀ1
which they have assigned to SeOO species. Even though we
might be tempted to assign the observed features at
1074.2(Ar) and 1073.7(N2) to TeOO isomer similar to SeOO
species, we have assigned them to the TeTeOO based on the
following reasoning: it is well known fact that Te2(g) is the
major species in the vapor phase over Te(s) [23]. In our
laser-ablation experiments too there is a very high probability
of formation of Te2, which might further react with O2 to
form TeTeOO according to the reaction (3).
4.3.6. Te2O4
Te þ O2 ! TeTOO
ð3Þ
DFT calculations have predicted a cyclic structure for the
Te2O4 species. Fig. 1p shows the structure of the Te2O4,
which contains four Te–O bonds in the ring and two Te–O
bonds in the axial positions, and Table 1 gives the structural
parameters, vibrational frequencies and the ZPE corrected
energies. We observed features at 881.4, 617.7, 538.6 in
As per the DFT calculations, the stretching fundamental
frequencies for the TeTeOO isomer (1159.3 cmꢀ1) is much
closer (ꢁ7.0%) to the experimental frequency than for
TeOO (1203.1 cmꢀ1; ꢁ11%) isomer. Hence, we assign the
observed features to TeTeOO.

246
K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
d
c
d
b
a
c
b
a
650
625
600
cm-1
575
550
525
900
850
800
750
cm-1
d
c
b
a
1150
1100
1050
1000
cm-1
Fig. 3. Matrix isolation infrared spectra of laser-ablated Te in the region 650–525, 900–750 and 1150–1000 cmꢀ1 using O2/Ar mixed matrix.
Concentration of O2 in the O2/Ar was 10%. (a) As deposited, (b) 25 K annealed, (c) photolysed and (d) 25 K annealed.
Table 5
species. The calculated frequencies for Te2O4 has the stron-
Infrared absorptions (cmꢀ1) observed for Te + O2 in argon matrix
gest features at 879.1, 617.2 and 534.9 cmꢀ1 which are lower
Frequencies (cmꢀ1
)
Assignments
by 0.3%, 0.1% and 0.6%, respectively, when compared with
the experimental frequencies.
1328.3
1111.4
1074.2
1039.0
886.2, 881.4
865.0, 858.7
841.4
823.1
782.5
662.5
617.7
TeO2, 2t1 ꢀ t2
TeO2, t1 + t2
Te2O2
O3
(TeO2)2
TeO3
TeO2, t3
TeO2, t1
TeO
The increase in Te2O4 features on photolysis can be
explained based on the fact that the TeO2 formation in
the matrix is increased on photolysis due to (1) Possible
insertion of Te atom into the oxygen molecule as per reac-
tion (4) and (2) Breaking of Te–Te bonds and possible rear-
rangement to form TeO2 and Te in the matrix as per
reaction (5). The excess TeO2 formed in the above reactions
in the matrix might undergo dimerization to form Te2O4
according to the reaction. (6)
TeOTe
(TeO2)2
(TeO2)2
Cyclic-TeTeO
538.6
591.6
UVhm
Te þ O2 ! OTeO
ð4Þ
ð5Þ
ð6Þ
TeTeOO U!Vhm OTeO þ Te
UVhm
argon and at 881.4, 619.6, 538.6 in N2 matrix. Fig. 5 (block A
and block B) shows the behavior of these features during
annealing cycle and photolysis in Ar and N2 matrices. As
can be seen, in both the matrices all the three features
behaved similarly during annealing cycle as well as on pho-
tolysis ascertaining that these features belong to the same
2ðOTeOÞ ! Te2O4
4.3.7. TeN
The calculations predict TeN fundamental to occur at
757.5 cmꢀ1. We observed split features in N2 matrix at

K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
247
d
c
d
b
a
c
b
973.5
a
650
625
600
575
550
525
1000
950
900
850
800
750
cm-1
cm-1
d
c
d
c
b
b
a
a
1150
1100
1050
1000
1900
1880
1860
1650 1600 1550 1500
cm-1
cm-1
Fig. 4. Matrix isolation infrared spectra of laser-ablated Te in the region 650–525, 1000–750, 1150–1000 and 1900–1500 cmꢀ1 using O2/N2 mixed matrix.
Concentration of O2 in the O2/N2 was 10%. (a) As deposited, (b) 25 K annealed, (c) photolysed and (d) 25 K annealed.
Table 6
SN [26] and SeN molecules [27,28]. Fig. 4 shows the infra-
red spectrum over the above regions when tellurium was
Infrared absorptions (cmꢀ1) observed for Te+O2 in nitrogen matrix
Frequencies (cmꢀ1
)
Assignments
laser ablated in the presence of 10% O2/N2. The occurrence
of spectral feature at 1657.6 and 2003ꢀ.4 cmꢀ1 are clear sig-
1874.6
2235.0
1616.2
1657.2
2003.4
1575.2
1108.0
1074.2
1042.9
973.5
NO
ꢀ
N2O
NO2
natures of the presence of N3 and N3 and (not shown) in
our laser ablation of Te with 10% O2/N2 experiment pro-
vides a strong support for the formation of TeN as was
observed in the case of UN [14]. Fig. 2a shows the structure
and Table 2 gives the ZPE corrected energy for the TeN
species.
ꢀ
N3ꢀ
N3
TeNO
TeO2, t1 + t2
Te2O2
O3
TeNTe
881.4
848.1
833.2
778.7
(TeO2)2
TeO2, t3
TeO2, t1
TeO
4.3.8. NTe2
DFT calculations predicted two possible isomers for
NTe2. Of these, the bent TeNTe structure is the global min-
ima. The angle between the Te–N–Te was calculated to be
143.7°, which is very similar to the bent SeNSe molecule
[27]. Fig. 2b–c show the structure of the isomers, Table 2
gives the vibrational frequencies, the geometries and the
ZPE corrected energies. The calculated Te–N stretching
frequency occurs at 860.9 cmꢀ1 which is 12% lower com-
pared to the experimentally observed feature at
973.5 cmꢀ1. The other isomer with a bent TeTeN structure
is less stable by 35 kcal/mol and the calculated vibrational
790.3
784.0
662.0
623.4/619.6
538.6
TeN site 1
TeN site 2
TeOTe
(TeO2)2
(TeO2)2
Cyclic-TeTeO
588.2
790.3 and 783.5 cmꢀ1. The calculated frequencies are lower
than the experimental values by 4.3% and 3.3%, respec-
tively. Similar site split feature has also been reported for

248
K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
1694.8 cmꢀ1. Experimentally, we observed a feature at
1.0
0.8
0.6
0.4
0.2
0.0
1575.7 cmꢀ1 in the as-deposited spectrum, which is lower
than the calculated value by about 7.5%. On photolysis
the intensity of this feature decreased considerably. We
assign the observed feature at 1575.7 cmꢀ1 to the N–O
stretching mode of the bent TeNO molecule analogous to
the SNO and SeNO species [26,27].
Block A
617.7
881.4
4.3.11. TexNy species
DFT calculations were also performed for the higher tel-
lurium nitrides as well. Two of these structures are given in
Fig. 2i–j and the corresponding parameters in Table 2.
Experimentally, we could not discern any features corre-
sponding to the higher Te–N clusters.
538.6
4
1
2
3
0.8
0.6
0.4
0.2
0.0
5. Comparison of different oxide and nitride species formed
between tellurium and selenium
619.6
Block B
Barbson et al. [24] studied the species formed when sele-
nium was discharged/heated with oxygen in argon matrix.
They observed SeO, SeO2, SeO3, (Se2)(O2), SeSeO, SeOO,
exocycle-Se2O2 and cis-OSeOO, with (Se2)(O2) being the
major species. In our experiments, we observed species
due to TeO, TeO2, TeO3, Te2O2, Te2O4 and TeTeO with
Te2O2 as the major species. As can be seen, the Te + O
analogs of SeOO, exocycle-Se2O2 and cis-OSeOO were
not observed. However, we could observe higher tellurium
oxide cluster (Te2O4). In Se2O isomers, bent SeSeO isomer
is the most stable one whereas in the case of Te2O the cyc-
lic-TeTeO isomer is the most stable species.
881.4
538.6
4
1
2
3
Experiments
Fig. 5. Areas of the different peaks in Ar matrix (block A) and N2 matrix
(block B) for various experimental conditions: (1) as deposited, (2)
annealed at 25 K, (3) photolysed and (4) annealed at 25 K after photolysis.
Concentration of O2 in the both the matrices was 10%.
Selenium with N2 forms [27,28] a variety of products
such as SeN, Se2N, NSe2þ, SeSeN, cis-SeSeNSe, trans-SeSe-
SeN and SeNO whereas in Te with 10% O2/N2 experiments
we could identify species only due to TeN, Te2N and TeNO.
We found no evidences for higher tellurium nitride clusters.
frequency occur at 830.5 cmꢀ1. Hence, we assign the fea-
ture observed at 973.5 cmꢀ1 to the bent TeNTe molecule.
6. Conclusion
4.3.9. N2Te
This study reports for the first time the matrix isolation
infrared spectra of the laser-ablated tellurium oxide species
in argon and nitrogen matrices. The primary reaction prod-
ucts obtained in the Ar and N2 matrices are Te2O2, TeO,
TeO2, Te2O and Te2O4. In N2 matrix, in addition to the
primary laser-ablated products, reaction products TeN,
TeNTe and TeNO were also observed. While the identifica-
tion of TeO and TeO2 species agreed with the Knudsen
cell-MI experiments [3], we also observed some exotic reac-
tion products such as Te2O2, cyclic-TeTeO and Te2O4 and
these features were corroborated with the help of computa-
tions. When compared to the reactivity of selenium and tel-
lurium towards nitrogen, tellurium is less reactive whereas
selenium forms host of higher selenium nitride species.
According to DFT calculations there are three possible
isomers for N2Te. Fig. 2e–f shows the structure of these
isomers. Of these, the linear TeNN and cyclic-TeNN iso-
mers have an infrared active N2 perturbation mode at
2195.4 and 2105.4 cmꢀ1. The other isomer, linear NTeN
is less stable by 150 kcal/mol and has a Te–N fundamental
at 881.4 cmꢀ1. Experimentally, we could not discern any
features corresponding to these isomers.
4.3.10. TeNO
Of the two possible isomers predicted by DFT calcula-
tions, the one with Te attached to NO is the global minima.
Fig. 2g–h shows the structures of these isomers. The bond
˚
distance between the Te and NO is 2.0 A and the bond
angle is 138.9°. These data indicate that the molecule is
bent and is similar to the structure of bent SeNO molecule
[27]. Calculations predicted a very strong fundamental
band for the NO stretching mode to occur at
Acknowledgements
V.K. gratefully acknowledges the grant of a research
fellowship from the Council of Scientific and Industrial

K. Sundararajan et al. / Journal of Molecular Structure 876 (2008) 240–249
249
R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J.
Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K.
Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslow-
ski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T.
Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challa-
combe, P.M. W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L.
Andres, C. Gonzalez, M. Head- Gordon, E.S. Replogle, J.A. Pople,
Gaussian 98, Revision A.9, Gaussian Inc., Pittsburgh PA, 1998.
[16] Basis sets were obtained from the Extensible Computational Chem-
istry Environment Basis Set Database, Version 02/02/06, as devel-
oped and distributed by the Molecular Science Computing Facility,
Environmental and Molecular Sciences Laboratory which is part of
the Pacific Northwest Laboratory, P.O. Box 999, Richland, Wash-
ington 99352, USA, and funded by the US Department of Energy.
The Pacific Northwest Laboratory is a multi-program laboratory
operated by Battelle Memorial Institute for the US Department of
Energy under contract DE-AC06-76RLO 1830.
Research (CSIR), India. We thank Dr. T.S. Lakshminara-
simhan, IGCAR, Kalpakkam for useful discussion in pre-
paring the manuscript.
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