ORIGINAL RESEARCH

Potential energy surface and thermochemistry for the direct gasphase reaction of germane and water

Bhaskar Mondal Æ Indranil Bhattacharyya ÆDeepanwita Ghosh Æ Abhijit K. Das

Received: 30 April 2009 / Accepted: 9 June 2009 / Published online: 25 June 2009

� Springer Science+Business Media, LLC 2009

Abstract Gas phase reaction between germane GeH4 and

water H2O was investigated at CCSD(T)/[aug-cc-pVTZ-pp

for Ge ? Lanl2dz for H and O]//MP2/6-31G(d,p) level.

Only the hydrogen elimination channels are monitored.

Within the energy range of 100 kcal/mol, we located nine

equilibrium and six transition states on the potential energy

surface (PES) of the Ge–O–H systems. GeH4 reacts with

H2O exothermically (by 2.37 kcal/mol) without a barrier to

form a non-planar complex GeH4�H2O which isomerizes

to GeH3OH�H2 and H2GeOH2�H2 with a barrier of

44.34 kcal/mol and 53.75 kcal/mol respectively. The first

step of hydrogen elimination gives two non-planar species,

GeH3OH and H2GeOH2 but germinol GeH3OH is found to

be more stable. Further thermal decomposition reactions of

GeH3OH involving hydrogen elimination have been stud-

ied extensively using the same method. The final hydrogen

elimination step gives HGeOH which can exist in cis and

trans forms. As the trans form is more stable, only the

trans form is considered on the potential energy surface

(PES) of the reaction. The important thermochemical

parameters (DrEtot ? ZPE), DrH and DrG for the H2

elimination pathways are predicted accurately.

Keywords Germane � Water � Hydrogen elimination �Thermochemistry � Potential energy surface (PES)

Introduction

Germane is mainly used in the semiconductor industry as

a source of germanium for deposition of epitaxial and

amorphous silicon–germanium alloy layers. The Si–Ge

layers in a multiple junction device efficiently capture red

and infrared photons and significantly enhance overall

solar energy conversion. The need for efficient, environ-

mentally friendly solar energy sources has increased the

demand for germane. There is also a growing demand for

germane gas for the production of Si–Ge semiconductor

devices. In one family of devices, germanium alloyed with

silicon produces a strained heterostructure when silicon is

deposited on the Si–Ge layer. This strained technology

provides significant benefits for the production of hetero-

junction bipolar devices able to engineer band gaps to

specific device required for high frequency optical net-

working, wireless and other communication applications.

Depending upon the applications, the structures of the

products can be monitored through fabricating conditions.

Germane is used as the precursor in the chemical vapor

deposition (CVD) process, which is the major manufac-

turing technique of Si–Ge thin film. The low deposition

temperature of the CVD/PECVD (plasma enhanced

chemical vapor deposition) process has a negative effect on

the quality of the product because the product at low

temperature contains significantly more water impurities

than those at high temperature. During the process of

fabrication, an elevated temperature is also required. At

this temperature water is involved not only as an impurity

but also as a reactant or by product [1–4]. The desirable

properties of the product can be obtained by examining the

effects of water concentration on the properties of the

product. Clearly, the reaction between germane and water

is the important underlying process for the quality control

of the product. In this article we have studied in detail the

mechanism of the underlying process, the reaction of ger-

mane with water that dictates the quality of the product. As

far as our knowledge goes the theoretical work in this field

B. Mondal � I. Bhattacharyya � D. Ghosh � A. K. Das (&)

Department of Spectroscopy, Indian Association for the

Cultivation of Science, Jadavpur, Kolkata 700032, India

e-mail: spakd@iacs.res.in

123

Struct Chem (2009) 20:851–858

DOI 10.1007/s11224-009-9483-3

is very limited. Suk Ping So studied the formation of

GeH3OH from the reaction between GeH2 and H2O and

its decomposition paths using the G2 molecular orbital

method [5]. Hu et al. [6] investigated the gas-phase reac-

tion between silane SiH4 and water using MP2 and

CCSD(T) methods and located various equilibrium and

transition states on the potential energy surface (PES) of

the Si–O–H system. Ibuta et al. [7] carried out ab initio

quantum chemical calculations for the self-decomposition

reaction and propagation reaction of germane. But no

theoretical or experimental work has been done so far to

study the mechanism of the direct reaction between GeH4

and H2O. To elucidate the H2 elimination pathways of

GeH4–H2O reaction occurred in CVD/PECVD, the present

theoretical work helps to explain the mechanism starting

from GeH4:H2O = 1:1 to all possible products via hydro-

gen elimination within the energy range 100 kcal/mol.

The hydrogen elimination pathways of the current

reaction can be designed as follows: the first step of

hydrogen elimination (reaction 1a and 1b) occurs from the

stable complex GeH4�H2O and the second step of hydrogen

elimination (reaction 2a and 2b) occurs from the stable

intermediate GeH3OH.

GeH4 þ H2O! GeH4 � H2O! GeH3OHþ H2 ð1aÞGeH4 þ H2O! GeH4 � H2O! H2GeOH2 þ H2 ð1bÞGeH3OH! H2GeOþ H2 ð2aÞGeH3OH! trans�HGeOHþ H2 ð2bÞ

Calculation details

Only the singlet PES of the lowest electronic state is inves-

tigated in this work. All the reactants, products and transition

states involved in the reactions was fully optimized at the

MP2[FC]/6-31G(d,p) level of theory. The literature shows

MP2 method works well for describing the reaction and

thermochemistry of these systems with small basis sets like

6-31G(d), 6-31G(d,p), 6-311G(2df,p), 6-31G(d,p) [8, 9]. We

choose the MP2 method with 6-31G(d,p) for geometry

optimization and frequency calculation [10]. Transitions

sates are located using synchronous transit-guided quasi-

Newton (STQN) methods. The normal mode analysis gives

‘all positive’ frequencies for equilibrium structures and ‘one

negative’ frequency for all transition states. The ‘one nega-

tive’ frequency confirms a first order saddle point and finally

intrinsic reaction coordinate (IRC) calculations were per-

formed to confirm the relationship of each transition states

with its reactant and product. Single point energy calcula-

tions with MP2[FC] and CCSD(T)[FC] methods were per-

formed to take into account the electron correlation effect on

single point energy and to get better electronic and therefore

relative energies. We used several basis sets 6-31G(d,p),

6-311 ??G(3df,3pd), cc-pVTZ and aug-cc-pVTZ-pp to

check the consistency of the calculated relative energy of the

species involved in the reaction. The relativistic effect due to

the heavy germanium (atomic no. 32) atom was taken into

account by using effective core potentials (ECP) aug-cc-

pVTZ-pp basis set for Ge and Lanl2dz basis sets for H and O

with CCSD(T)[FC] method [11, 12]. This type of calculation

with mixed basis set is reported in literature [13]. All the

relative energies are corrected with ZPE obtained by fre-

quency calculation on each species involved at the MP2[FC]/

6-31G(d,p) level. For the calculation of thermodynamic

parameters, the highly accurate energy prediction model like

G2(MP2) was used. The G2(MP2) model is essentially a

composite method and the steps involved are mentioned

elsewhere [14]. All thermodynamic parameters were calcu-

lated without taking into account the internal rotations of the

molecules and a frequency scaling factor of 1.00 was used.

All the electronic structure calculations were performed with

the Gaussian 03 quantum chemical package and thermo-

chemical calculations were performed by MOLTRAN code

[15, 16].

Results and discussions

The total energies calculated at three different theoretical

levels, namely MP2[FC]/6-31G (d,p), MP2[FC]/cc-pVTZ

and CCSD(T)[FC]/cc-pVTZ together with dipole moments

(D) and rotational constants (A, B and C) for all the species

are listed in Table 1. The various stationary point and

transition state structures studied here are depicted in the

reaction scheme presented in Figs 1 and 2. Figure 3 con-

tains the transition state structures with the vectors showing

their imaginary frequency. All the equilibrium and transi-

tion state structures were located by MP2[FC]/6-31G (d,p)

level of theory and are shown with their geometrical

parameters calculated at the same level of theory. The

hydrogen elimination reactions pathways of germane are

divided into two parts (reactions 1 and 2) and is shown in

Figs. 1 and 2. The combined singlet PES calculated at the

CCSD(T)/[aug-cc-pVTZ-pp for Ge ? Lanl2dz for H and

O]//MP2/6-31G (d,p) level of theory is presented in Fig. 4.

Pathways from GeH4 ? H2O to GeH3OH and H2GeOH2

and interconversion of the intermediates

At the initial stage, GeH4 reacts with H2O exothermically

without a barrier to form a complex GeH4�H2O in which

GeH4 and H2O are weakly bound. This association makes the

system stable by stabilization energy of -2.37 kcal/mol. In

this complex, the Ge–H bond length increased by 0.004A and

852 Struct Chem (2009) 20:851–858

123

the tetrahedral symmetry of GeH4 part is lost. The weak

interaction in this complex is maintained by a Ge–O distance

of 3.137A. In the successive discussions, GeH4 ? H2O

system is taken as the initial reactant and relative energies of

the species involved in the reaction are measured with

respect to this system. Now the complex GeH4�H2O can be

activated to the TS1 transition state with activation energy of

*44.34 kcal/mol. The TS1 contains a ring structure having

an –H–H– dihydrogen bond and a Ge–O distance of 2.016A,

shortened by 1.121A than in GeH4�H2O. The transition

vector is dominated by the motion of the two bridging

hydrogen, one is 1.895A from Ge and the other is 1.149A

from the O atom. The transition vector with the imaginary

frequency is shown in Fig. 3. The TS1 results a complex

GeH3OH�H2, a molecular combination of GeH3OH and H2,

from which elimination of hydrogen yields germinol

GeH3OH. GeH3OH produced in this way retains three ori-

ginal hydrogen atoms bonded to germanium as in GeH4 and

only one of the hydrogen atoms is replaced by an OH group.

The complex GeH3OH�H2 get stabilized by -15.17 kcal/

mol relative to the starting system indicates that the process

is thermodynamically favored. Alternatively, the activation

of GeH4�H2O complex to TS2 requires activation energy of

*53.75 kcal/mol which is *9.41 kcal/mol greater than the

former activation pathway. The transition state TS2 having a

non-planar structure contains only one hydrogen atom bon-

ded to the germanium and the other three hydrogen atoms are

dative bonded to Ge. The interaction between Ge and O in

TS2 is maintained by a Ge–O distance of 2.922A which is

0.215A shorter than that in GeH4�H2O. The transition vector

with imaginary frequency is dominated by the three dative

bonded hydrogen atoms which are 1.682, 2.189 and 1.707A

apart from Ge atom. The TS2 with the imaginary frequency

is shown in Fig. 3. The elimination of H2 from TS2 produces

another complex, namely H2GeOH2�H2, a weakly bonded

complex of H2GeOH2 and H2. In H2GeOH2 molecule, OH2

part is dative bonded to H2Ge part with a distance of 2.206A.

The dissociation of the germane-water complex through this

way requires *9.41 kcal/mol more energy and the product

H2GeOH2 is less stable than GeH3OH by 36.43 kcal/mol.

So, an interconversion of H2GeOH2 to GeH3OH is very

much likely and the interconversion may occur with a small

activation barrier of 27.58 kcal/mol. The conversion

H2GeOH2 � GeH3OH may occur via transition state TS3

which is a ring structure having an –H– bridge between Ge

and O and the structure is maintained by a Ge–O distance of

2.029A. The transition vector for the imaginary frequency in

TS3 is governed by the displacement of the bridged hydrogen

atom which is 1.620A from Ge and 1.368A from O. The

transition state TS3 is shown in Fig. 3 with the imaginary

Table 1 Electronic energies (Etot), dipole moment and rotational constants (A, B & C) of the species

Species Symma Etot (hartree)b Etot (hartree)c Etot (hartree)d ZPE

(kcal/mol)bD (Debye)d A (GHZ)b B (GHZ)b C (GHZ)b

GeH4�H2O C1(0) -2151.895101 -2154.263848 -2154.310551 35.08 1.814 61.90 3.35 3.33

TS1 C1(1) -2151.817297 -2154.184659 -2154.229523 32.74 1.706 46.28 7.61 7.27

GeH3OH�H2 C1(0) -2151.899962 -2154.263980 -2154.308037 32.34 1.868 29.22 7.23 6.35

TS2 C1(1) -2151.800303 -2154.174379 -2154.221711 32.67 2.237 55.23 3.74 3.68

H2GeOH2�H2 C1(0) -2151.847659 -2154.207454 -2154.255832 32.65 3.772 51.41 5.20 5.01

GeH3OH Cs(0) -2150.739183 -2153.097828 -2153.134239 24.01 1.715 71.07 9.80 9.65

TS3 C1(1) -2150.635231 -2151.995428 -2153.032186 21.90 1.554 78.41 8.07 7.93

H2GeOH2 C1(0) -2150.687462 -2153.041053 -2153.081800 24.96 3.904 77.04 6.62 6.57

TS4 C1(1) -2150.607321 -2152.973149 -2153.005636 20.18 4.330 59.69 11.04 10.58

H2GeO�H2 C1(0) -2150.659723 -2153.014046 -2153.046963 18.48 5.025 30.02 9.44 8.00

TS5 C1(1) -2150.633440 -2152.996659 -2153.036123 21.48 1.613 66.15 9.74 9.50

HGeOH�H2 C1(0) -2150.691479 -2153.044138 -2153.083383 20.79 1.586 16.78 9.89 6.70

H2GeO C1(0) -2149.500300 -2151.848482 -2151.873702 10.95 4.946 152.65 12.79 11.80

TS6 C1(1) -2149.421504 -2151.771276 -2161.793824 9.21 4.250 142.03 11.76 10.92

HGeOH C1(0) -2149.532575 -2151.879733 -2151.911152 13.04 1.456 157.45 10.78 10.09

GeH4 Td(0) -2075.667743 -2077.941575 -2077.974870 19.75 0.000 80.48 80.48 80.48

H2O C2t(0) -76.2197857 -76.318642 -76.332205 13.73 2.038 803.32 437.7 283.3

H2 D?h(0) -1.156611 -1.164642 -1.172284 6.59 0.000 1862.3

a Symmetry of the species, the number of imaginary frequency are in parenthesesb MP2/6-31G(d,p) calculationsc MP2/cc-pVTZ//MP2/6-31G(d,p) calculationsd CCSD(T)/cc-pVTZ//MP2/6-31G(d,p) calculations

Struct Chem (2009) 20:851–858 853

123

transition vector. Suk Ping So showed theoretically the

existence of H2GeOH2 and its conversion to GeH3OH with

an energy barrier of 28.3 kcal/mol in the reaction between

GeH2 and H2O [5]. Their result is very much close to our

value 27.58 kcal/mol.

Thermal dissociation of GeH3OH via hydrogen

elimination

As discussed by Suk Ping So [5], Germinol can dissociate

thermally by eliminating H2, H, OH and H2O. Here we will

discuss only the dissociations via H2 elimination pathways.

GeH3OH, formed from a thermodynamically favorable i.e.,

exothermic pathway in the reaction between GeH4 and

H2O can be activated to TS4 with high activation energy

barrier of 72.60 kcal/mol. The transition state TS4 has a

ring structure similar to TS1 containing –H–H– bridge

between Ge and O with a triangular GeH2 moiety. The

Ge–O distance is shortened by 0.080A in TS4 from the

parent compound. As expected, the transition vector is

governed by the displacement of the two bridged hydrogen

atoms that are datively bonded to the Ge and O by a dis-

tance of 1.869 and 1.510A respectively. The hydrogen

elimination from TS4 gives a triangular planar species

H2GeO in which the Ge–O distance is 1.676A. This path-

way is endothermic in nature by 34.82 kcal/mol.

In another possible pathway, the activation of GeH3OH

to TS5 requires 14.67 kcal/mol less activation energy than

that needed for activation to TS4. The transition state TS5

is reactant like with only one hydrogen is datively bonded

to Ge and the transition vector is governed by the three

hydrogen atoms bonded to Ge. The elimination of H2 from

TS5 gives trans-HGeOH which is more stable than its cis

isomer. So only the trans isomer is shown in the combined

PES. The trans-HGeOH is more stable than cis-HGeOH by

0.33 kcal/mol. Moreover, trans-HGeOH is more stable

than H2GeO formed through the other pathway. Now an

exothermic conversion from H2GeO to trans-HGeOH is

very much likely and it may occur through a transition state

TS6 with an energy barrier of 47.85 kcal/mol. The transi-

tion state TS6 has distorted triangular geometry with Ge–O

bond-length 1.772A and two different H–Ge–O bond

angles. The transition vector in TS6 is governed by the

movement of the two hydrogen atom bonded to Ge.

Energetics and thermodynamics

The relative energy of the species involved in the reaction

of GeH4 and H2O are summarized in Table 2. The energy

Ge H

H

H

H

109.47

1.528O

H H103.86

0.961

GeH4 H2O

TS2

TS1

+ H H0.733

+ H H0.733

H2 H2

GeH3OH

+ Ge

H

H

HH O

H

H

1.532

1.5263.137

0.963

103.7

110.3

108.6

111.4

H

Ge

H

O

H

H

1.584

1.574

2.2060.966

92.4

87.0

85.9

109.5

109.1

106.2Ge O

H

HH

H1.533

1.5231.806

0.964

103.9

111.7

109.3 110.5

Ge

H

H

O

H

H

1.537

1.542

1.620 1.368

2.029 0.973105.285.1

107.7

Ge

H

H

H

O

H

H

H

1.5471.530

1.5251.895

1.088

1.149

0.9712.016

104.9

106.4

115.7

81.3

76.6

117.3

Ge

H

H

H

H

O

H

H1.568

1.682

2.189 1.707

2.9220.963

87.0

93.7

104.2

GeH4·H2O

H2GeOH2

TS3

Fig. 1 Reaction scheme for the

reaction GeH4 ? H2O to

GeH3OH and H2GeOH2 with

geometries at MP2/6-31G(d,p)

level

854 Struct Chem (2009) 20:851–858

123

of the species and their relative energy are highly basis set

dependent and hence the choice of basis set is very

important for this study. The ab initio methods MP2 and

CCSD(T) are used to check the consistency of the

calculated relative energy. From the previous studies on

germane and its derivatives it is observed that the ab initio

Ge O

H

HH

H1.533

1.5231.806

0.964

103.9

111.7

109.3 110.5

+ +

H

Ge

H

O

1.532

1.676113.5

123.2

H

Ge O

H

1.575 1.813

0.967

92.3

109.6

H

Ge

H

O

H

H

1.533

1.533

1.726

1.869

0.926

1.51

111.7

123.5

123.6

46.6

64.1 Ge

H

H

H

O

H

1.551

1.530

1.733

1.812

0.965112.8110.7

112.2

43.7

Ge

H

H

O1.560

1.561

1.772

57.9

118.1

161.0

GeH3OH

H H0.733

H H0.733

TS4TS5

H2GeO

H2 H2

TS6

trans-HGeOH

Fig. 2 Reaction scheme for the

reaction GeH3OH to H2GeO

and trans-HGeOH with

geometries at MP2/6-31G(d,p)

level

Fig. 3 Vectors showing the

vibrational modes with the

imaginary frequency for the

transition states with geometries

at MP2/6-31G(d,p) level

Struct Chem (2009) 20:851–858 855

123

MP2 method works well for these systems with small basis

set like 6-31G(d), 6-31G(d,p), 6-311G(2df,p). We chose

6-31G (d,p) basis for geometry optimization as well as to

minimize the computational cost. The relative energy cal-

culated for GeH4�H2O complex matches well with the value

of Ibuta et al. [7]. To verify the consistency of the relative

energies and to get better energies the basis is improved to

6-311??G(3df,3pd) then to cc-pVTZ. It is observed from

the Table that the relative energy calculated by MP2/6-

31G(d,p) method for GeH4�H2O complex is -3.15 kcal/

mol whereas that calculated by MP2/6-311??G(3df,3pd)

method is ?0.64 kcal/mol and by the MP2/cc-pVTZ

and CCSD(T)/cc-pVTZ methods are -0.67 kcal/mol and

-0.59 kcal/mol respectively. Thus the exothermicity of the

initial association of GeH4 and H2O is not well explained by

the MP2 and CCSD(T) methods in conjunction with the

6-311??G(3df,3pd) as well as the correlation consistent

cc-pVTZ basis sets. This is may be due to the relativistic

effect of Ge atom. To remove the discrepancy between

these values and to incorporate the relativistic correction,

we use effective core potential (ECP) aug-cc-pVTZ-pp

basis set for Ge which incorporates the relativistic effect

due to heavy atom and Lanl2dz basis set for H and O. The

relative energy obtained by CCSD(T) method with relativ-

istic basis set is -2.37 kcal/mol. It is important to note that

the trend in relative energy obtained by MP2/6-31G(d,p)

method is similar to that obtained by CCSD(T)/aug-cc-

pVTZ-pp method. Also, the calculation of relative energy by

CCSD(T)[FC] method with ECP basis set is consistent with

the work of Ibuta et al. who used B3LYP method in con-

junction with 6-31G(d,p) basis set. The present analysis is

based on the zero point correction obtained from MP2[FC]/

6-31G(d,p) calculation. The detail analysis of energetics

shows that among the four hydrogen elimination channels,

only the first one through which formation of GeH3OH is

thermodynamically favored i.e., exothermic in nature. The

other three channels are endothermic.

The nature of the four hydrogen elimination channels

is further explained by examining reaction energy

(DrEtot ? ZPE), enthalpy (DrH298.15) and Gibbs free energy

(DrG298.15). For the calculation of these thermodynamic

parameters, the G2(MP2) method along with MP2, is also

employed to verify the accuracy of the calculation. The

reaction energies in terms of different thermodynamic

parameters are listed in Table 3. The first H2 elimination

reaction is exothermic which is supported by the calculation

of reaction energy, enthalpy and Gibbs free energy. It may

be noted that the all three energies calculated by G2(MP2)

method are 5 kcal/mol lower than those obtained by MP2

method. The remaining three H2 elimination reactions are

endothermic. Among the three endothermic H2 elimination

reactions, the maximum endothermicity is observed for the

H2 elimination from GeH3OH via H2GeO formation. The

similar endothermicity is reflected form the calculated

MP2 reaction energy, enthalpy and Gibbs free energy. The

G2(MP2) Gibbs free energy for the second and fourth H2

elimination reaction differs by about 12 kcal/mol.

The activation energy barrier for the hydrogen elimi-

nation as well for the isomerisation processes are tabulated

in Table 4. We applied MP2 and CCSD(T) methods to

calculate the activation energies. The third set of data in

Table 4 is obtained by CCSD(T) method in conjunction

-20

0

20

40

60

80

(5.68)

(66.14)

(18.30)

(5.93)

(41.4)

(18.41)

(56.07)

(19.9)

(47.48)

(-16.52)

(19.75)

(51.38)

(-15.17)

(-2.37)

(41.97)

(0.00)

HGeOH

TS6

H2GeO

-H2

-H2

HGeOH:H2

TS5

H2GeO:H

2

TS4

TS3

H2GeOH

2

GeH3OH

-H2

-H2

H2GeOH

2:H

2

TS2

GeH3OH:H

2

TS1

GeH4:H

2O

GeH4 + H

2O

Rel

ativ

ene

rgy

(kca

l/mol

)

Reaction Coordinate

Fig. 4 Schematic potential

energy surface for the

GeH4�H2O reaction via H2

elimination at CCSD(T)/[aug-

cc-pVTZ-pp for Ge ? Lanl2dz

for H and O]//MP2/6-31G(d,p)

level

856 Struct Chem (2009) 20:851–858

123

with the ECP aug-cc-pVTZ-pp basis set. Among four H2

elimination reactions, the lowest activation energy barrier

of 44.34 kcal/mol is calculated for the first reaction

where the complex GeH4�H2O produces GeH3OH by

H2 elimination. The highest activation energy barrier

72.60 kcal/mol is obtained for the reaction where GeH3OH

dissociates to H2GeO and H2.

Conclusions

In this article a direct gas phase reaction between germane

GeH4 and H2O has been studied in detail using ab initio

MP2 and CCSD(T) methods. A 1:1 GeH4�H2O complex is

formed exothermically via a barrier less process. Four

hydrogen elimination pathways are identified on the basis

of reported stable Ge–O–H systems. The formation of

germinol, GeH3OH by hydrogen elimination from ger-

mane-water complex is thermodynamically most feasible

process with lowest activation energy among all possible

hydrogen elimination channels considered for the gas

phase reaction. If more energy is provided to the non-

planer GeH4�H2O complex, the H2GeOH2 species may be

formed through H2 elimination. The important intermediate

Table 3 Summary of the reaction energies, enthalpies and gibbs free energies for the proposed H2 elimination reactions

DrEtot ? ZPE DrH298.15 DrG

298.15

MP2 G2(MP2) MP2 G2(MP2) MP2 G2(MP2)

GeH4 ? H2O ? GeH3OH ? H2 -8.72 -3.61 -8.49 -3.28 -8.09 -3.13

GeH4 ? H2O ? H2GeOH2 ? H2 24.68 28.19 25.34 29.03 24.57 27.97

GeH3OH ? GeH2O ? H2 44.49 45.42 46.13 46.93 37.96 38.90

GeH3OH ? HGeOH ? H2 26.33 22.20 27.92 23.73 19.74 15.75

MP2 = MP2[FC]/6-31G(d,p) calculations

Table 2 Relative energies

(kcal/mol) for the species at

different theoretical levels

Species Relative Energies (kcal/mol)

MP2/

6-31G(d,p)

MP2/6-311

??G(3df,3pd)

MP2/

cc-pVTZ

CCSD(T)/

cc-pVTZ

CCSD(T)/

aug-cc-pVTZ -pp

GeH4 ? H2O 0.00 0.00 0.00 0.00 0.00

GeH4�H2O -3.15 0.64 -0.67 -0.59 -2.37

TS1 43.33 46.35 46.67 47.93 41.97

GeH3OH�H2 -8.95 -2.81 -3.50 -1.75 -15.17

TS2 53.75 51.90 52.88 52.75 51.38

H2OGeH2�H2 24.17 30.21 32.26 31.32 19.75

GeH3OH ? H2 -8.72 -3.90 -4.30 -2.53 -16.52

TS3 ? H2 54.40 57.37 57.85 59.40 47.48

H2OGeH2 ? H2 24.68 30.27 32.30 31.32 19.90

TS4 ? H2 70.18 69.43 70.11 74.33 56.07

H2GeO�H2 ?H2 35.60 42.02 42.75 46.70 18.41

TS5 ? H2 55.10 57.05 56.65 56.50 41.40

HGeOH�H2 ? H2 17.39 22.04 25.58 26.16 5.93

H2GeO ? 2H2 35.77 41.65 42.40 46.37 18.30

TS6 ? 2H2 83.47 86.95 89.10 94.75 66.14

HGeOH ? 2H2 17.61 21.41 24.86 24.97 5.86

Table 4 Activation energy barrier (DrE#) of the species involved in

the H2 elimination reaction

Reactions Energy of activation DrE# (kcal/mol)

I II III

GeH4�H2O ? GeH3OH ? H2 47.35 48.50 44.34

GeH4�H2O ? H2GeOH2 ? H2 53.56 53.16 53.75

GeH3OH ? H2GeOH2 62.14 61.95 64.00

GeH3OH ? H2GeO ? H2 74.40 76.86 72.60

GeH3OH ? HGeOH ? H2 60.95 59.03 57.92

H2GeO ? HGeOH 46.70 48.38 47.85

I: MP2/cc-pVTZ//MP2/6-31G(d,p)

II: CCSD(T)/cc-pVTZ//MP2/6-31G(d,p)

III: CCSD(T)/aug-cc-pVTZ-pp//MP2/6-31G(d,p) calculations

Struct Chem (2009) 20:851–858 857

123

GeH3OH is rather stable at ordinary temperatures towards

the different hydrogen elimination channels. Kinetics may

favor the dissociation of GeH3OH to H2GeO and trans-

HGeOH via hydrogen elimination at ordinary tempera-

tures. In PECVD process at low temperature, the films

contain more germinol and water impurities and are less

dense than films deposited or grown at high temperature.

The substrate temperature has the largest effect on the

germinol and water impurity concentrations. The germinol

concentration is an important factor in determining the film

properties. The hydroxyl group of the germinol is polar and

hence an increase in germinol concentration causes to

increase the permittivity and loss. The refractive index also

decreases if the germinal concentration increases. There-

fore the desired properties of the film may not be obtained

unless the formation of germinol impurity is prevented.

Our theoretical work in this regard may help to understand

the underlying mechanism of the reaction between ger-

mane and water that controls the quality of the product.

Acknowledgments We thank Aneesur Rahman Centre for High

Performance Computing of IACS for providing us the computational

facility. B. M gratefully acknowledges the Council of Scientific and

Industrial Research (CSIR), Government of India for a junior research

fellowship. Thanks are due to the reviewer for his valuable comments

to improve the manuscript.

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